DALLAS — Senator Amy Klobuchar of Minnesota, who entered the Democratic presidential race with an appeal to moderate voters and offered herself as a candidate who could win in Midwestern swing states, has decided to quit the race and endorse a rival, former Vice President Joseph R. Biden Jr., according to a person close to Ms. Klobuchar.
Ms. Klobuchar will appear with Mr. Biden at his rally in Dallas Monday night. The decision comes one day after former Mayor Pete Buttigieg of South Bend, Ind., departed the race, and after weeks of Democratic Party hand-wringing about a crowded field of moderate candidates splitting a finite field of centrist votes, allowing Senator Bernie Sanders of Vermont to march forward unopposed among progressives and amass delegates.
Shortly after the news broke about Ms. Klobuchar, Harry Reid, the former Senate majority leader, said in a statement that he would endorse Mr. Biden as well.
Ms. Klobuchar, despite a strong third-place finish in New Hampshire, lagged her moderate rivals in every other state and was often seen as a candidate siphoning support. Though she had varying levels of support across the Super Tuesday map, polling within reach of leading candidates in some predominantly Republican states with open primaries, but it is unclear how much of a boost any of her rivals will see in the wake of Ms. Klobuchar’s exit, or where she may direct her 7 delegates.
The senator from Minnesota shocked her rivals with a surprising third-place finish in New Hampshire, placing ahead of better-known candidates like Senator Elizabeth Warren of Massachusetts and Mr. Biden.
But aside from New Hampshire, Ms. Klobuchar struggled deeply, lagging all of her competitors in Iowa, Nevada and South Carolina. Though her campaign received a much-needed influx of cash after New Hampshire — $12 million in just over a week — it proved too little, too late for the campaign to rapidly scale up and compete with her better funded and better organized rivals.
The Klobuchar campaign was constantly rescheduling events, oftentimes releasing public advisories for an event with less than 24 hours advance notice. One “get out the caucus” rally in Nevada at Rancho High School attracted less than 100 people. Days before, Pete Buttigieg, the former mayor of South Bend, Ind., brought more than 1,200 to the same school.
Ms. Klobuchar was forced to cancel a rally in her own backyard Sunday night, after protesters from Black Lives Matter and other local civil rights groups took over the stage in St. Louis Park, Minn. They were calling attention to the case of Myon Burrell, a black man convicted of murder as a teenager while Ms. Klobuchar was county attorney.
Recent news reports have raised questions about the case, including numerous reported flaws with the prosecution. Ms. Klobuchar, while stopping short of apologizing, has called for the case to be reviewed.
The frantic scramble to build out a national campaign followed a diligent and relentless focus on Iowa. Ms. Klobuchar was the first 2020 candidate to visit all 99 counties, and spent most of her time, money and field staff deployed to the state. Her self-described “gritty” effort in Iowa kept her on the debate stage, meeting polling thresholds in early states rather than in national polls.
With a calm but prosecutorial demeanor mixed with a dry sense of humor, Ms. Klobuchar slowly built momentum through consecutive debate performances, seeing immediate spikes in cash and volunteers. But she never experienced a true “viral moment” — something she lamented in the closing days of her campaign while speaking in Nashville — forcing her to run a threadbare operation in every state outside of Iowa.
Ms. Klobuchar famously kicked off her campaign in the middle of a blizzard a year ago, her nearly hourlong presidential announcement marked by the piles of snow that accumulated on her hatless head as she debuted her centrist message.
On the campaign trail, she would refer frequently to her snowy beginnings as she continually pitched her Midwestern roots as a presidential credential, arguing that her “I live here” heartland appeal could win back states like Michigan, Ohio and Wisconsin, which President Trump carried in 2016.
As a perpetual and direct contrast to the vocal liberal base of the Democratic Party, Ms. Klobuchar stubbornly stuck to a moderate message, one she hoped would appeal to independents and moderate Republicans. She vocally opposed “Medicare for all,” and built one of her most popular stump speech lines around defending the Affordable Care Act, claiming that it was “10 points more popular than the guy in the White House Right now.”
Her campaign also amounted to a bet that in a deeply polarized electorate, a bipartisan voting record could still be viewed as an asset in the Democratic electorate. She regularly touted the more than 100 bills that she passed during her 14-year Senate career, and name-checked Republican senators that she frequently worked with in her stump speech.
But her bipartisan record also carried some risk; she was among the most likely Democratic senators to vote for a Trump judicial nominee, a point seized on by rivals like Mr. Buttigieg in debates.
She struggled more than any other candidate to attract support in minority communities, particularly among black voters. She faced calls from local civil rights organizations in Minneapolis, including the N.A.A.C.P. chapter, to suspend her campaign after news reports raised questions about a murder conviction of a black teenager under her tenure.
As she made her final run, Ms. Klobuchar abandoned South Carolina, the first state to vote with a meaningful black population, four days early. And her Super Tuesday campaign swing through 11 different states avoided the two biggest, and most diverse: Texas and California.
But the senator kept her message upbeat throughout the campaign, and she always had her New Hampshire finish to point to, as she did in Nashville a few days before Super Tuesday.
“We have been really, really beating the odds,” she said.