Tonight’s Democratic Debate: Live Updates From Houston

How to watch: 8 p.m. to 11 p.m. Eastern on ABC, Univision and on streaming services.

Moderators: The debate will be hosted by George Stephanopoulos, David Muir, Linsey Davis and Jorge Ramos.

Candidates: Former Vice President Joseph R. Biden Jr., Senator Elizabeth Warren, Senator Bernie Sanders, Senator Kamala Harris, Mayor Pete Buttigieg, the entrepreneur Andrew Yang, Senator Cory Booker, former Representative Beto O’Rourke, Senator Amy Klobuchar and former housing secretary Julián Castro.

It is the presidential campaign that brought hundreds of reporters and photographers to this sprawling, and still-steamy-in-September, city. But while Texas Democrats are happy to host the third presidential primary debate, it is not the White House race that many of them are most excited about.

One year after they beat a pair of veteran House Republicans, Democrats here are downright giddy about the possibility of picking up even more seats in 2020. That’s because of what has been called the “Texodous” — the decisions of five, so far, House Republicans from Texas to retire rather than seek re-election.

“They see the handwriting on the wall,” said Gilberto Hinojosa, the Texas Democratic Chair.

Three of the G.O.P. lawmakers who are retiring had won re-election by only five points or less and hail from districts filled with the sort of suburban and nonwhite voters who are uneasy with President Trump and are nudging this state toward the political center.

Even though he won Texas by nine points, Mr. Trump’s standing has plummeted in Texas: a new Quinnipiac poll found that 50 percent of the state’s voters disapprove of his job performance and 48 percent said they would definitely not vote for him next year.

While few officials in either party believe Democrats could capture the state from Mr. Trump next year, their prospects up and down the ticket here could depend in part on who they nominate.

And Mr. Hinojosa said most Texas Democrats were less focused on policy issues than who can make the best case against Trump. “They want a candidate that can beat him,” he said. “That’s the number one priority.”

But as for his own priorities, Mr. Hinojosa said he was more focused further down the ticket.

“Our main goal in Texas right now is to flip the state House,” he said, noting that many of the nine seats they are hoping to pick up in the legislature are in those same suburban districts where they may be able to win more congressional races.

And why is he so focused on state house races going into a year when Democrats have a chance at the White House? Because if Democrats control one chamber of the legislature they could at least slow Republican attempts to redraw legislative boundaries for another decade after next year’s census.

That’s the word from most, if not all, the Democratic nominees and their campaigns on Thursday, no one wanted to detail exactly how they were preparing to differentiate themselves from each other. In Houston, where several candidates and their staffs happen to be staying at the same hotel in the downtown area, the matchup of Mr. Biden, Mr. Sanders and Ms. Warren is the talk of happy hours and pre-debate events.

But it’s the candidates outside the top three that are promising the most fireworks.

Ms. Harris, Mr. Booker and Mr. O’Rourke are trying to present themselves as the most future-oriented candidates. Ms. Harris is expected to go on offense. Mr. O’Rourke will focus on offering a generational alternative to his establishment rivals, and Mr. Booker is likely to pitch similarly unifying themes.

If that sounds familiar, it’s because Democrats say they want to resist the urge to pit themselves against one another. So how will audiences get differentiating moments? We have three hours of debate to find out.

For months, Ms. Warren has risen through the polls without much interference from the other candidates seeking the 2020 Democratic presidential nomination. Rivals praised the plans she offered, even as they chafed at having to always answer questions about them.

That time is near an end.

There has been a marked shift lately on how others in the field — particularly those far behind her in the polls — approach Ms. Warren, with increasing skepticism about her battery of policy proposals.

“This election is not just about our plans, it’s about our heart and gut,” Mr. Booker said Saturday in New Hampshire.

The tougher questions Ms. Warren will face are about whether she is too liberal to win a general election. Mr. Buttigieg calls for “real solutions, not more polarization” in an Iowa TV advertisement he debuted this week. Ms. Klobuchar said in an interview this week that “you don’t just want to win, you want to win big.”

The problem for the low-polling candidates is that Ms. Warren has now established herself as the candidate of ideas — ideas Democrats like. Along the way she has become very popular herself, a figure they may have allowed to become too imposing to take down.

In the first debate, Mr. Buttigieg defended his record on race relations at the South Bend Police Department. In the second one, he faded into the background while Ms. Warren and Mr. Sanders owned the conversation about health care.

Now, as his campaign begins spending down his field-leading financial war chest, Mr. Buttigieg’s debate challenge is to shift from curiosity to serious candidate. He’s been a nonentity the first two times Democrats have debated in the presidential primary and he can’t afford a third tepid showing.

The challenge for the 37-year-old is how to present himself as a breath of fresh air and steward for a new generation of politics without getting his hands dirty by attacking others onstage. His contrast with Mr. Biden is implicit — the former vice president is nearly 40 years older — but if he is going to make the argument that he can build a broader coalition than his more liberal opponents, that may require some explaining to a still-skeptical electorate.

Below the marquee matchup between Mr. Biden and Ms. Warren, perhaps the most intriguing subplot onstage will be among the candidates stuck in the single-digits in polling trying to position themselves as the leading, less ideological alternative to Mr. Biden.

For now, Ms. Warren and Mr. Sanders seem to dominate the left. Who can emerge as Mr. Biden’s leading rival for the center-left?

The various candidates each have different theories of the case. Mr. Buttigieg has been making a generational argument, though he has increasingly waded into more centrist and unifying grounds. “We need real solutions, not more polarization,” he said in his first TV ad that aired in Iowa.

Ms. Harris, who confronted Mr. Biden directly in the first debate, has tried to position herself as a tough former prosecutor who could take on President Trump one-on-one. Ms. Klobuchar is probably closest to Mr. Biden ideologically and has sold herself as a Midwestern moderate (who would also be a history-making first female president). Mr. Booker has, like Mr. Biden, promised to unify the nation and positioned himself as a healer. But while Mr. Biden has focused chiefly on beating Mr. Trump, Mr. Booker has said from the start that is “a floor not a ceiling” for 2020.

If other candidates are itching to go after Ms. Warren, Mr. Sanders has shown no inclination to squabble with the other leading liberal in the race.

At his debate preparations in Colorado this week, Ms. Sanders has focused on what he has been talking about his entire political career: limiting the power of corporations, installing a single-payer health care system and requiring billionaires to pay more to subsidize a broader social safety net.

That’s not likely to draw him into much of a contrast with Ms. Warren, but it may lead him into a fight with Mr. Biden, either as a tag-team partner with Ms. Warren or on his own.

Mr. Biden, aside from ideological differences, is Mr. Sanders’s chief competitor for Democratic primary voters. Their supporters tend to be lower-income, less educated and far less tuned in to the day-to-day machinations of the presidential campaign than those who back candidates like Ms. Warren or Mr. Buttigieg.

So for Mr. Sanders, a clash with Ms. Warren does less good than showcasing his ideological contrast with Mr. Biden and peeling support away from the former vice president.

Unlike many onstage in Houston, the question for Ms. Harris is not whether she can have a breakout moment. She can. She already has. The question — a harder one to answer — is whether she can turn a strong debate performance into sustained political momentum.

Ms. Harris’s first debate takeover of Mr. Biden of his past work with segregationists and busing led to a quick rise in the polls that quickly faded.

In the second debate, Ms. Harris arrived as the subject of attacks herself — most sharply by Representative Tulsi Gabbard of Hawaii, who will not be onstage this week — and delivered a more uneven performance.

Ms. Harris has herself among the top-tier candidates but that is the kind of phrase often best left for others to utter. Her mandate on Thursday is to show that to be the case, and then have public polling demonstrate the same.

Our colleague Michael Grynbaum wrote today about ABC’s decision not to delay Thursday’s broadcast, leaving censors helpless to bleep any blurted profanities:

Faced with profligate profanities on the campaign trail — and at least one candidate who publicly threatened to work blue on its airwaves (ahem, Beto O’Rourke) — ABC News issued a warning this week to the 10 Democrats appearing on the debate stage in Houston on Thursday: Keep it clean, folks.

“We wanted to take this opportunity to remind you that, as the debate will air on the ABC broadcast network, we are governed by Federal Communications Commission indecency rules,” Rick Klein, the network’s political director, wrote in a memo forwarded to campaigns by the Democratic Party.

“Candidates should therefore avoid cursing or expletives in accordance with federal law,” Mr. Klein added, presumably sighing deeply.

The fact that the debate will be carried on regular broadcast airwaves — instead of cable — means the network could face penalties from federal regulators if obscenities are uttered.

Jonathan Martin and Astead W. Herndon contributed reporting from Houston.