LAS VEGAS — In the nearly two weeks since her standout debate performance in New Hampshire, the momentum behind Senator Amy Klobuchar of Minnesota had encountered nary a pothole.
With a stack of endorsements from local and national newspapers lured by her centrist platform, a surprising third-place finish in New Hampshire and a cash infusion of $12 million, Ms. Klobuchar was suddenly awash in “top-tier candidate” punditry chatter and attracting a fresh — and often first — look from voters.
But with that sudden success came a withering torrent of criticism on the debate stage Wednesday night from rivals like Senator Elizabeth Warren of Massachusetts and Pete Buttigieg, the former mayor of South Bend, Ind.
Both of them poll ahead of Ms. Klobuchar nationally and in some key Super Tuesday states like California, but they are seeking to halt her rise and win over her supporters before that pivotal day, as Senator Bernie Sanders of Vermont threatens to build an insurmountable delegate lead.
“It’s like a Post-it note,” Ms. Warren said, as she criticized Ms. Klobuchar’s health care platform. “Insert plan here.”
“You voted to make English the national language,” Mr. Buttigieg said, as he turned to face Ms. Klobuchar, standing to his left. “Do you know what message that sends, in as multilingual a state as Nevada, to immigrants?”
In Ms. Klobuchar, who campaigns on protecting and improving the Affordable Care Act and has deeply personal stories about fighting for longer hospital stays after giving birth, Ms. Warren faces a new competitor for suburban, college-educated women, largely moderates, who have formed a new and crucial bloc of support for Democrats after President Trump’s election.
Mr. Buttigieg sees a candidate running an overall similar playbook to his — holding town halls and interviews on Fox News, knocking down “Medicare for All” proposals, making direct appeals through a Midwestern lens to independents and some Republicans — and who is closing in on his rise as a moderate alternative to Mr. Sanders.
“I think people make a mistake when they say that Warren and Sanders are the ones competing in a lane, because the voters that are going to put Warren in a position to be competitive are deciding not between Sanders and Warren, but between Buttigieg, Klobuchar and Warren,” said Addisu Demissie, a Democratic strategist and the former presidential campaign manager for Senator Cory Booker of New Jersey.
“The three of them, I think, are in a fight in a lot of ways for those college-educated voters,” he said.
Mr. Demissie said that Mr. Sanders’s passionate and devoted following made up roughly a third of the Democratic base, and that pulling voters away from him would be nearly impossible. So the other three, he said, would most likely look to “the college-educated, primarily white but not exclusively white voters” to build their support.
In New Hampshire, Ms. Klobuchar narrowly carried the college-educated vote, according to exit polls.
Ms. Klobuchar has cited her steady stream of newspaper endorsements as evidence that she can appeal to those who hope to see a more moderate candidate take on Mr. Trump.
Though only a single metric with unknown impact on voters, to look at the endorsements Ms. Klobuchar has racked up — nine so far, double the amount of most of her rivals — is to get a window into how Ms. Klobuchar long laid the foundation for what appeared to be a very rapid rise from obscurity to winning national delegates.
Sitting in front of largely white and well-educated editorial boards across the country, made up of journalists who often have lengthy résumés of their own, Ms. Klobuchar was able to construct a portrait of her candidacy as one that was built on a bipartisan record in Congress and can appeal to independents.
“Her electability and her bipartisan history of being able to navigate the Washington system was one of the biggest factors in our endorsement,” said Brendan McQuaid, the publisher of The New Hampshire Union Leader. “She’s been down there and done it and known the ins and outs of how Capitol Hill works, which is something that is crucial for a functioning government.”
The numerous editorials praising Ms. Klobuchar’s competence and experience perhaps served as a signal to her rivals that they couldn’t let her record go unchallenged on the debate stage.
Mr. Buttigieg, for example, quickly and aggressively seized on an embarrassing gaffe by Ms. Klobuchar, when she could not name the president of Mexico during an interview with Telemundo.
He attacked her votes for many of Mr. Trump’s judicial nominees during the first two years of his presidency, as well as her support of Mr. Trump’s pick to head Customs and Border Protection, someone Mr. Buttigieg said was “one of the architects of the family separation policy.”
Ms. Klobuchar poses a threat to Mr. Buttigieg’s Midwestern appeal, and her pitch that her roots in the Midwest would help win back the heartland states that voted for Mr. Trump in 2016 was met with wide agreement from editorial boards.
“Electability, we understand the electoral map,” said Dan Borenstein, the editorial page editor of The East Bay Times in California. “And as the editorial says to Californians, the general election isn’t going to be decided here. It’s going to be decided in Wisconsin, Michigan and Pennsylvania, probably.”
Left unsaid by many of the boards, however, was Ms. Klobuchar’s dismal polling with people of color, particularly black and Latino voters. Her endorsements from newspapers in Iowa and New Hampshire, states with largely white populations, were more concerned with her immediate future in those contests, and the national newspapers believed she could make up lost ground.
“That is a big concern,” said Lisa Falkenberg, the vice president-editor of opinion at the Houston Chronicle, who said Ms. Klobuchar needed to be making more direct appeals to black voters in particular regarding health care. But, she argued, there’s still time.
“Realistically, black voters are known to be pragmatic,” Ms. Falkenberg said. “They are also looking for a candidate that can beat Donald Trump.”
Ms. Klobuchar also faced tough questioning Wednesday from Chuck Todd, one of the debate moderators, over her record as a county prosecutor in Minnesota, particularly whether a black teenager was wrongly convicted of murder during her tenure as the Hennepin County attorney.
Framed as a question about whether her record as county prosecutor would erode trust with black and Latino voters, Ms. Klobuchar defended her handling of the case, reiterated her call for it to be reviewed, and pledged to work to earn support.
“I have the support of African-Americans in my community in every election,” she said. “I had strong support and strong support of leadership. And that’s because I earned it. And this is going to be on me to earn it.”
Here in Nevada, as Ms. Klobuchar seeks to remain relevant in a state with a decidedly diverse population, her campaign began running an ad in Spanish that pointed to yet another endorsement, from The Las Vegas Sun.
In fact, nearly every ad run by the Klobuchar campaign in the past few weeks has touted one of her newspaper endorsements. Her recent seven-figure ad buy in seven Super Tuesday states features two new ads that boast of her endorsements from The New York Times — which she shared with Ms. Warren — and The Sun.
Editors at The Sun recognized that Ms. Klobuchar, as well as Mr. Buttigieg, faced an uphill battle with Latino voters in the state. But searching to identify something that could help her break through, they pointed to yet another facet of her experience in Washington: her work on immigration reform.
“Her work on comprehensive immigration reform in the Senate was something that struck us as being commendable, especially in southern Nevada where that issue is so critical for us,” said Ric Anderson, the paper’s editorial page editor.
He added that he thought her relative lack of national stature was one reason she hadn’t made inroads among people of color in Nevada.
“We didn’t really necessarily focus on the appeal to minority voters because of the uphill climb that she and Mayor Pete Buttigieg had just in getting where they are now in terms of recognition,” Mr. Anderson said. “We do see potential there.”