Elizabeth Warren makes her electability pitch.

Credit…Jordan Gale for The New York Times

DAVENPORT, Iowa — Senator Elizabeth Warren was asked, yet again, the question on Sunday that has bogged down her candidacy in Iowa and elsewhere in recent months: whether a candidate from the more moderate wing of the Democratic Party would more easily defeat President Trump.

“I think the old ways of looking at things just don’t work anymore,” Ms. Warren said.

Then, as she did at last week’s debate, she invoked her own electoral history — beating a popular Republican incumbent, then-Senator Scott Brown, in 2012 — the ambitions of her agenda and her gender.

“Can we just address it right here? Women win,” she said, explaining that the “world changed” with Mr. Trump’s election and the mass protest marches led by women the day after his inauguration.

“Women candidates have been outperforming men candidates since Donald Trump was elected,” she said. “We took back the House and we took back statehouses around the nation because of women candidates and the women who get out there and do the hard work to get it done.”

She added that her focus on corruption could “pull in Republicans.”

“We’re going to win it by drawing the distinction, the sharpest distinction between the most corrupt administration in history and a Democrat who is willing to get out there and fight corruption,” she said.

PERRY, Iowa — Bernie Sanders and Joseph R. Biden Jr. are fighting over yet another issue: climate change.

After days of back-and-forth jabs over Social Security, the two leading candidates have turned to attacking each other over their plans to fight climate change.

“Well Joe, you’re wrong,” Mr. Sanders said at an event in Perry on Sunday. “Many leading scientists agree with our plan and in a few days we’re gonna have a long list of scientists who agree with our plan.”

Mr. Sanders’s remark came in response to Mr. Biden’s comment two days ago denouncing Mr. Sanders’s plan. “There’s not a single solitary scientist that thinks it can work,” Mr. Biden said on Friday.

Mr. Sanders’s sweeping plan aligns with the Green New Deal and involves reducing domestic carbon emissions by at least 71 percent by 2030.

The two men represent the two factions of the Democratic Party, and have often dealt each other glancing blows. But more recently, they have landed more direct hits over Social Security. Mr. Sanders has also gone after Mr. Biden over his vote to authorize the war in Iraq.

ANKENY, Iowa — It would have been in 1973, if Maxine Goldstein recalls correctly, and she would have been 16 or 17.

Joe Biden was a new senator reeling from the deaths of his wife and daughter. Ms. Goldstein was on Capitol Hill for a congressional workshop program, and she wanted to meet him more than anyone.

It was “his warmth, his passion, his sincerity” that drew her to him, she said. Mr. Biden spoke with her in his office for about 15 minutes — “he was remarkably generous,” she said — and someone took a photo of them.

On the back, Mr. Biden wrote:

Maxine —

Please come back and visit

Joe Biden

USS

So she did Saturday night, 47 years later, at a conference center just north of Des Moines, 350 miles from her home in St. Louis.

Ms. Goldstein, now 63, is not an Iowan. Missouri doesn’t vote until after Super Tuesday. She isn’t even positive she’s going to vote for Mr. Biden, though she is leaning that way. But she wanted to see him.

And how did it go?

“It’s everything that I imagined,” she said, her husband smiling beside her. “He’s exactly now as he was then.”

DES MOINES — If it’s Sunday, it’s shopping time at Mercado Iowa Market, a small swap meet of sorts at El Malecon Event Center in south Des Moines. The mercado features food of all sorts — carne asada tacos, cheese-oozing pupusas and tlacoyos heaped with nopales.

So just what does all that food have to do with the upcoming Iowa caucuses? The market is perhaps one of the best places to see evidence of the growing Latino community in the state, which has more than doubled in the last two decades.

That growth is likely to affect the caucus — or “el caucus,” as it is known in Spanish. More Spanish speakers than ever are expected to show up to caucus night this year. And for the first time, the state Democratic Party is offering six Spanish-language satellite caucus sites, in an attempt to increase participation.

The problem? Party officials are still scrambling to find enough bilingual Spanish speakers to work at those sites and others around the state.

Last weekend, we spent time with one interpreter as she joined a few other community activists for a local a caucus training. Vanessa Marcano-Kelly, a native of Venezuela, became a citizen just last year and will participate in her first caucus next month.

Ms. Marcano-Kelly is a precinct captain for the Sanders campaign, one of just a few designated so far for the bilingual caucus sites. But as she learned more about the process last week, she wondered just who should have her loyalty on caucus night — the campaign or individual voters? And how could anyone be sure that everything at the bilingual caucus sites would operate smoothly?

Credit…Tamir Kalifa for The New York Times

With Joe Biden still leading most national polls, his rivals, especially Bernie Sanders, are increasingly hitting out at his decades-long record.

And as Mr. Biden has defended himself, emphasizing his standing among black voters and his foreign policy experience, he has made some misleading claims.

We fact-checked some of his statements on Social Security, birth control, North Korea and his role in the civil rights movement. Read more here.

HARTSVILLE, S.C. — If you live in South Carolina, you could be forgiven for thinking that Tom Steyer is the leading Democratic challenger to President Trump.

That’s because Mr. Steyer is everywhere in the state — TV commercials, Facebook ads, old-fashioned mailers through the postal system.

A hedge-fund billionaire from California, he is using his vast wealth to lavish money on black businesses in particular, hiring dozens of African-American staff members and spending generously with black-owned news organizations.

So far, it seems to be paying off. A Fox News survey this month showed Mr. Steyer in a surprisingly strong position in South Carolina — in second place with 15 percent of the vote.

An impressive showing in the Feb. 29 primary by Mr. Steyer could chisel into support for former Vice President Joseph R. Biden Jr., who is the clear front-runner in polls here.

Mr. Steyer’s focus on courting black voters seems to have earned him some good will, or at least positive media attention.

But some experts question the wisdom of Mr. Steyer’s spending here, and whether his money could be put to better use. Nonprofit groups and community organizations always need more funding; the Democratic presidential field does not necessarily need more candidates who are unlikely to win the nomination.

“If I’m running that campaign, I’m thinking it’s great that after all these tens of millions of dollars we’re finally starting to show some movement,” said Lachlan McIntosh, a Charleston-based Democratic consultant. “But my goodness, it is worth it?”

Read more here.

Credit…Tamir Kalifa for The New York Times

DES MOINES — A new CBS News poll released Sunday shows Senator Bernie Sanders of Vermont and former Vice President Joseph R. Biden Jr. neck-and-neck in Iowa eight days before the caucuses.

The poll, which was conducted from Jan. 16-23 and has a margin of error of plus or minus 3.9 percentage points, showed Mr. Sanders with 26 percent support and Mr. Biden with 25 percent, a statistically insignificant difference. Former Mayor Pete Buttigieg of South Bend, Ind., was also very close, at 22 percent.

Senator Elizabeth Warren of Massachusetts had 15 percent support, and Senator Amy Klobuchar of Minnesota had 7 percent. Nobody else had more than 1 percent support.

Candidates must get at least 15 percent support to be considered viable in a precinct; if they are below that threshold in the first vote, their supporters must realign themselves with a viable candidate. Only those who exceed 15 percent are eligible to win delegates, some of which will be awarded at the state level and some of which will be awarded in each of Iowa’s four congressional districts.

The CBS poll paints a somewhat different picture than a New York Times/Siena College poll of likely caucusgoers released on Saturday. That poll showed essentially the same amount of support for Mr. Sanders — 25 percent — but gave him a clearer lead over his competitors, showing Mr. Buttigieg at 18 percent, Mr. Biden at 17, Ms. Warren at 15 and Ms. Klobuchar at 8. The margin of error was plus or minus 4.8 percentage points.

PERRY, Iowa — Senator Bernie Sanders opened his remarks at his first town hall meeting of the day on Sunday with a slightly wistful interlude about what could have been.

“A few weeks ago, I would not have told you that I would be spending the last week of the campaign in Washington, D.C.,” he said.

The Vermont senator planned to spend the lead-up to the Iowa caucuses much as he spent it four years ago — criss-crossing the state, greeting thousands of potential voters and holding, by his estimation, 20 or 30 events.

Instead, like the three other senators running for president, Mr. Sanders will likely spend much of the next week marooned in the Senate chamber, listening to President Trump’s lawyers make their arguments.

While this isn’t ideal, his team believes Mr. Sanders’s brand and established organization in the state will be strong enough to withstand his absence. Recent polling has buoyed their hopes: A series of state and national polls show Mr. Sanders emerging as a late-breaking leader in the contest, consolidating support from liberals and benefiting from a divided moderate wing.

Mr. Sanders said he expects the momentum to continue until the caucuses. “The reason we are going to win here in Iowa is we have the strongest grass-roots movement of any campaign,” he said.

DES MOINES — Former Vice President Joseph R. Biden Jr. has not been a favorite of newspaper editorial boards so far, and Mr. Biden lost out on the coveted Des Moines Register endorsement on Saturday. But his campaign emerged from the day with a different endorsement to trumpet, from The Sioux City Journal in northwest Iowa.

The Journal’s case for Mr. Biden focused on his ability to pose a strong challenge to President Trump in the general election — an argument that is central to Mr. Biden’s candidacy. The Journal suggested Mr. Biden was well positioned to attract support not only from Democrats, but also from independents and from “disgruntled Republicans.”

“We view Biden as a pragmatist — and we believe his pragmatism is an attribute,” the newspaper wrote in its endorsement. “We refuse to believe middle-of-the-road compromise should be or is a relic of the past.”

The Journal also expressed a positive view of Senator Amy Klobuchar of Minnesota and urged Mr. Biden to consider her as his running mate if he becomes the Democratic nominee.

Northwest Iowa is a heavily Republican area, and it has not been a top focus of campaigning for Democratic presidential candidates. But The Journal’s track record bodes well for Mr. Biden. The newspaper endorsed Al Gore in the 2000 primary race and Barack Obama in the 2008 contest, both of whom went on to win the Iowa caucuses and become the Democratic nominee. The Register, on the other hand, endorsed Bill Bradley in 2000 and Hillary Clinton in 2008.

This time around, The Register gave its endorsement to Senator Elizabeth Warren of Massachusetts. Also on Saturday, The New Hampshire Union Leader endorsed Ms. Klobuchar.

Credit…Jordan Gale for The New York Times

DAVENPORT, Iowa — Patrick Peacock, an alderman on the Davenport city council, said before a gymnasium filled with more than 300 people Sunday morning that he had the high honor of introducing the next president of the United States: Senator Elizabeth Warren.

Then he tried to get the crowd fired up.

“El-Liz-A-Beth! El-Liz-A-Beth! El-Liz-A-Beth! El-Liz-A-Beth!” he exhorted.

The crowd tried. But four syllables do not an easy chant make — a fact that Ms. Warren acknowledged when she jogged out to the familiar tunes of Dolly Parton’s “9 to 5.”

“Next time, I’m going to get a more chantable name,” Ms. Warren joked.

Luckily, she has some ready-made options: Ms. Warren was known as Betsy growing up and later as Liz.

The first time we interviewed the Democratic presidential candidates, late last spring, we had a pile of yes-or-no, either-or policy questions to ask, many of them representing litmus-test issues at the heart of Democratic politics: single-payer health care and foreign wars, wealth concentration and tech regulation.

Our second round of interviews was different. For starters, we asked fewer candidates to participate, inviting only the ones with a realistic shot at accumulating a substantial number of delegates.

And we asked them, for the most part, a different genre of questions, exploring not just policy issues but also their ideas about leadership and the presidency.

Our hope was to produce a set of interviews that would guide voters trying to make a difficult final decision about which candidate they’d like to put in the country’s most powerful job.

Take a look.

Credit…Jim Wilson/The New York Times

DES MOINES — The entrepreneur Andrew Yang qualified for the next Democratic debate with a string of four strong polls released in quick succession on Saturday and Sunday.

Two polls of New Hampshire voters — one from CNN and the University of New Hampshire, and the other from NBC News and Marist — showed Mr. Yang at 5 percent, the minimum to qualify for the debate.

A national Fox News poll also showed him at 5 percent. And a national ABC News/Washington Post poll released Saturday found him at 7 percent, his best showing ever in a debate-qualifying survey.

Mr. Yang, who did not qualify for the last debate, is the seventh candidate to qualify for the next one. He had long since met the Democratic National Committee’s other qualification requirement: a minimum of 225,000 donors.

“America has spoken,” Mr. Yang’s campaign chief, Nick Ryan, said in a statement Sunday morning. “Voters clearly missed Andrew Yang’s presence in the most recent debate, and now they are making sure he will be on the debate stage in New Hampshire. The race for the nomination has only just begun, and Andrew Yang is going to keep fighting for all Americans to have their voices heard.”

Mr. Yang will join former Vice President Joseph R. Biden Jr.; former Mayor Pete Buttigieg of South Bend, Ind.; Senators Amy Klobuchar of Minnesota, Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts; and the former hedge fund executive Tom Steyer onstage in Manchester, N.H., on Feb. 7, four days before the New Hampshire primary.

STORM LAKE, Iowa — Pete Buttigieg had one of northwest Iowa’s most coveted surrogates introduce him before a town-hall-style event Saturday night at Buena Vista University: David Johnson, a former state senator who in 2016 quit the Republican Party when Donald J. Trump won its presidential nomination.

Mr. Johnson, who didn’t seek re-election in 2018, represents exactly what Mr. Buttigieg says he’d bring as the Democratic presidential nominee: support from former Republicans disgusted with Mr. Trump.

The only problem? Mr. Johnson endorsed Senator Amy Klobuchar of Minnesota in September. He’s planning to serve as a precinct captain for Ms. Klobuchar in his hometown, Ocheyedan, just over the border between Iowa and Minnesota.

That didn’t stop the Buttigieg campaign from informing reporters that Mr. Johnson, who introduced Mr. Buttigieg as “the next president of the United States,” had “announced his support for him.”

Mr. Johnson said after the event that he’s still backing Ms. Klobuchar.

“They’re two good candidates,” he said. “I’m just happy with someone from the Midwest.”

Mr. Johnson said he was asked to introduce Mr. Buttigieg after the scheduled introducer had car trouble and missed the event. He called Mr. Buttigieg the next president, he said, because that’s just something you say when someone visits Iowa.

“It’s a courtesy,” he said. “I would do it for anyone who had a D behind their name.”

Despite his affection for them, Mr. Johnson doesn’t expect either Mr. Buttigieg or Ms. Klobuchar to win the state’s caucuses.

“My prediction is Senator Sanders,” he said, referring to Senator Bernie Sanders of Vermont, who is leading in the latest Iowa polling.

“There’s a lot of things that have happened, and Secretary Clinton didn’t do any good to tamp down his case,” he said, referencing critical remarks Hillary Clinton made last week about her former primary rival.

“I tell you, that guy’s people are going to be out there with a vengeance.”

AMES, Iowa — The impeachment trial scrambled plans for the senators competing in the Democratic primary race. They would normally be blitzing Iowa in the final days before the caucuses, but they instead spent much of the past week in Washington, serving as jurors for the trial of President Trump, before returning to Iowa on Saturday.

Bernie Sanders took something of a lighthearted tone about his Washington detention.

“I am really delighted to be here tonight,” he told a crowd in Ames, after being introduced by the filmmaker Michael Moore and Representative Alexandria Ocasio-Cortez of New York. “You don’t know how delighted I am, because last night, I didn’t know that I would be here!”

Earlier in the night, he also briefly touched on his time in Washington.

“As you well know, we have had to radically change our schedule in the last week — kind of toss it into the garbage can and begin anew,” he said at a stop on Marshalltown. “But we are going to be back here in Iowa in the next week every moment that we possibly can.”

It is not clear how much, or even if, being away from the trail will affect Mr. Sanders and the other senators in the race. For now, he is surging in Iowa, and gaining momentum in other early states.

A New York Times/Siena College poll released on Saturday showed Mr. Sanders in a commanding first place, with 25 percent support — 7 percent ahead of his nearest opponent. A poll on Sunday from CNN showed him leading in New Hampshire, too.

MUSCATINE, Iowa — The Des Moines Register endorsed Senator Elizabeth Warren for the Democratic presidential nomination on Saturday night, calling her “the best leader for these times.”

The newspaper, Iowa’s largest and most influential, gave Ms. Warren a boost just over a week before the caucuses on Feb. 3, when Iowans will take part in the first nominating contest of the primary cycle.

The Register’s endorsement landed as Ms. Warren worked her way through her selfie line after a town-hall-style event in Muscatine, Iowa.

She did not find out until after she took the final picture, when her communications director, Kristen Orthman, pulled her aside to share the news.

Ms. Warren leapt back in excitement — pulling her hands to her chest, as if to say, “what, me?” — and then pumped both hands in the air and did a little dance. Ms. Orthman then appeared to show Ms. Warren the editorial on her phone.

Ms. Warren gulped down a sip of coconut water, one of her campaign trail staples, and headed over to a gathered group of reporters and microphones with a smile.

“I just heard and I’m delighted,” Ms. Warren said of the endorsement. “It really means a lot to me. I’m very happy.”

The endorsement was one of three released in quick succession Saturday evening. The New Hampshire Union Leader backed Amy Klobuchar, writing: “Her work in Washington has led to the passage of an impressive number of substantive bills, even as the partisan divide has deepened.

And The Sioux City Journal in Iowa gave its support to Joseph R. Biden Jr., calling him “the candidate best positioned to give Americans a competitive head-to-head matchup with President Trump.”

DES MOINES — We’re approaching the final week before the Iowa presidential caucuses, and the Democratic campaign pulsed with a newly urgent and frenetic energy on Sunday morning as the five top candidates descended on the state and a crush of new polls and endorsements came out.

Here’s how to think about it:

There are eight days left until the caucuses next Monday night, and there are plenty of undecided or wavering Iowa voters who have a history of breaking late in favor of a candidate. Senator Bernie Sanders of Vermont is ahead in Iowa in the latest New York Times/Siena College poll, while he and former Vice President Joseph R. Biden Jr. are effectively tied in a new CBS News poll in Iowa published on Sunday. Senator Elizabeth Warren of Massachusetts just won The Des Moines Register’s endorsement and Mr. Biden picked up the Sioux City Journal’s backing.

Most of the campaign events on Sunday are in the Democratic population centers of Des Moines, Cedar Rapids and Davenport, and the candidates are making a case for their policy ideas but also for their electability.

While Mr. Sanders almost tied Hillary Clinton in Iowa in 2016, the competition is much greater now, but also fluid. There are two liberal candidates — Mr. Sanders and Ms. Warren — competing for Iowa’s big progressive vote, which often turns out energetically on caucus night. Three moderates — Mr. Biden, former Mayor Pete Buttigieg of South Bend, Ind., and Senator Amy Klobuchar of Minnesota — are largely carving up the centrist vote.

Yes, there is overlap among the candidates. Ms. Warren and Mr. Buttigieg are both chasing upper-income, college-educated, left-leaning Democrats, for instance. But polls indicate that Mr. Sanders could be on a path to putting together a plurality of caucusgoers next Monday night.

The main takeaway from the new polls — in addition to the Iowa polls, there were two national surveys and two New Hampshire primary polls — is that Mr. Sanders and Mr. Biden are now co-front-runners, with Mr. Biden having the edge nationally and Mr. Sanders in New Hampshire (as well as Iowa). Mr. Buttigieg and Ms. Warren have strength in New Hampshire as well, but their fate in the Feb. 11 primary there is partly dependent on how well they do in Iowa.

We are out with the top five candidates across Iowa today and will bring you updates throughout the afternoon and evening.