AMES, Iowa — On Tuesday, when Democrats had hoped to focus Americans squarely on President Trump’s impeachment trial, many in the party were instead watching in alarm and dismay as a fresh spat erupted between Hillary Clinton and the candidate she defeated in 2016, Sen. Bernie Sanders.

In comments published early Tuesday, Clinton left open the possibility that she might not support Sanders if he is the party’s nominee. The remarks unleashed fresh angst less than two weeks before the Iowa caucuses amid a flurry of other attacks dividing the presidential candidates and their allies.

Sanders (I-Vt.) has been engaged in battles with rivals on various fronts over the past week squabbling with Sen. Elizabeth Warren (D-Mass.) over whether he once said a woman could not be president, attacking former vice president Joe Biden with an out-of-context video about Social Security and issuing a rare apology after a top surrogate called Biden corrupt.

The conflicts have reignited Democratic fears that, whoever becomes the nominee, the party will rupture as it did four years ago, when divisions between the Clinton and Sanders camps marred the primaries and the summer convention, and were blamed by many for contributing to her loss to Trump that November.

“Nobody wants to re-litigate 2016. I don’t want Democrats focused on the last campaign; I want to focus on the next campaign,” said Terry McAuliffe, the former Virginia governor and former head of the Democratic National Committee. “People have to check their attacks. We can’t get in the mud pit where Donald Trump wants to be. Let’s not be playing on his turf.”

“If Bernie is the nominee,” he added, “everyone has to rally.”

Rebecca Katz, a liberal New York-based consultant, put the blame squarely on Clinton.

“This is bringing up old wounds,” Katz said. “It’s four years later, and the nominee in 2016 is not saying for certain whether they are going to support the nominee in 2020? That is unacceptable.”

Katz added: “This is Hillary Clinton. She had to know how explosive these remarks would be. And she did it anyway. And she did it now.”

“There’s enough post-traumatic stress out there already,” said former senator Barbara Boxer (D-Calif). “I think it’s best if we just move forward. But everybody has a right to say what’s in their heart.” She added that the one benefit of the intensifying primary is it allows voters to see battle-tested candidates, saying, “Whatever they are getting now they’re going to get 10 times worse in the general.”

Clinton’s comments, published just hours before Democrats began to make their case on impeachment in Washington and as several candidates launched a full day of campaigning here in Iowa, came in an interview promoting a documentary about her that will premiere at Sundance Film Festival on Saturday.

In the film, she offered a blunt assessment of Sanders, casting him as a career politician who has deceived his supporters into believing he could implement change.

“He was in Congress for years,” she said. “. . . Nobody likes him, nobody wants to work with him, he got nothing done. He was a career politician. It’s all just baloney, and I feel so bad that people got sucked into it.”

When asked in the interview with the Hollywood Reporter if that assessment still held, she responded, “Yes, it does.” Asked if she would support him if he won the nomination, she demurred, saying, “I’m not going to go there yet. We’re still in a very vigorous primary season. ”

She also criticized the willingness of his supporters to antagonize his political rivals.

It’s “not only him, it’s the culture around him,” she said. “It’s his leadership team. It’s his prominent supporters. It’s his online Bernie Bros and their relentless attacks on lots of his competitors, particularly the women. And I really hope people are paying attention to that because it should be worrisome that he has permitted this culture — not only permitted, [he] seems to really be very much supporting it. And I don’t think we want to go down that road again where you campaign by insult and attack and maybe you try to get some distance from it, but you either don’t know what your campaign and supporters are doing or you’re just giving them a wink.”

The comments triggered an outburst of criticism that flew across social media. Tommy Vietor, a former aide to President Barack Obama, tweeted that Clinton’s comments were “inexcusable” and the entire party needed to get behind the nominee, Sanders or not.

“Don’t kick up this . . . right before Iowa, especially after complaining about Bernie’s lack of support in 2016,” he wrote, noting that he was “TERRIFIED” about the party not being united in the general election.

A Clinton spokesman, Nick Merrill, responded to say that Clinton isn’t committing to any candidate in the primary and pointed to her record of working for Democrats, including former opponents like Obama.

“Let’s all take a deep breath, give her the benefit of the doubt for once, & look at history,” he wrote on Twitter.

Clinton late Tuesday mocked the hubbub she had created and seemed to suggest support for Sanders if he is the nominee.

“I thought everyone wanted my authentic, unvarnished views!” she tweeted. “But to be serious, the number one priority for our country and world is retiring Trump, and, as I always have, I will do whatever I can to support our nominee.”

Clinton’s comments seemed to feed into a growing concern among more-moderate and establishment Democrats that Sanders, an enduring and energetic force if a polarizing one, could damage the party if he captured the nomination. Others, however, worried that the convulsion could further alienate Sanders’s supporters, many of whom believe the 2016 race was stacked against him and fear the same happening in 2020.

“No one loves Hillary Clinton more than I do, but those remarks are not helpful,” said Ed Rendell, the former Pennsylvania governor. “Whoever wins, we have to get behind them. There’s no time this year for Democrats to resolve old grievances.”

Jen Psaki, a veteran Democratic consultant and former top Obama aide, said that it was clear Clinton “hasn’t buried the hatchet, and she needs to bury the hatchet.”

“There are a number of things that can simultaneously be true,” she said. “One, she shouldn’t have said it; two, it represents the view of many Democrats; and, three, he’s always been underestimated.”

The Sanders style of campaigning has increasingly grated on Biden and his campaign, who view his tactics as unfair and out of bounds. Sanders’s campaign aides promoted an out-of-context video of Biden that suggested he agreed with the proposals of then-House Speaker Paul D. Ryan (R-Wis.) to cut Social Security. Sanders said over the weekend that he wished they had shown the fuller context but stood by his criticisms of other comments by Biden on entitlements.

On Monday, a top Sanders ally wrote an op-ed saying that “Biden has a big corruption problem and it makes him a weak candidate.” Sanders apologized for the critique.

Some Democrats lamented that Sanders has not faced enough scrutiny, even as he has been repeatedly underestimated by some party leaders.

“What Hillary is saying is a general concern I have and a lot of other people have, too,” said Rep. Tim Ryan (D-Ohio), a former presidential candidate who has endorsed Biden. “Socialism and taking away people’s private health care and, you know, all these things that make it very very difficult to beat Donald Trump in the industrial states we need to win. Hillary knows that better than anybody, how hard that is. To me, she’s articulating a concern that a lot of us have.”

Besides his squabbles with Biden, Sanders also has exchanged barbs with Warren over her claim that Sanders told her during a private 2018 meeting that a woman wouldn’t defeat Trump — a claim Sanders has denied. The disagreement spilled onto the presidential debate stage last week.

Although the disagreements left some Democrats quaking, others found a bright side.

“I love it,” said Bakari Sellers, a former state legislator from South Carolina. “Politics is a contact sport. Unfortunately, Democrats think politics is tiddlywinks, which is why we got drummed by Donald Trump, who plays by no rules. We have to get tougher.”

He added: “Who is anyone to say Hillary Clinton can’t say whatever the hell she wants to say? It’s clear she has a visceral disdain for Bernie Sanders.

“The debate is invigorating,” he said. “Nothing is out of bounds.”

Other Democratic presidential candidates sought to gain advantage through comparison. The super PAC supporting Biden saw an opening to distinguish its candidate, releasing a new ad called “The Storm” that shows choppy ocean waters amid text that reads, “Joe Biden. A President to Right the Ship,” and says he’s “The Democrat Who Can Lead Through the Storm.”

Former South Bend, Ind., mayor Pete Buttigieg, who has campaigned as someone who can turn the page on controversies of the past, reiterated that argument.

“I didn’t love going through the experience of our party divisions in the past,” Buttigieg said in response to questions about Clinton. “I’m focused now on making sure that the future is better.”

Until the recent battling, the 2020 race has been tame by comparison to 2016 — a fact that some held on to.

“In the immediate short term, all of these soap-operatic outbursts are a distraction,” said Robert Zimmerman, a top donor and DNC member from New York. “Do I think it’s going to prevent us from being united? I don’t think so. But we have to be very disciplined about it. Because it wouldn’t be the first time we saw a fight get out of control.”

In Iowa, a representative of those mostly too young to take part in the past disputes demanded that her elders cease the current ones.

“Everyone stop fighting about 2016 please thanks!!!!!!!!!!!!! No need for that!!!!!!!!!!! Our President is literally on trial right now!!!!!!!!! Focus on 2020!!!!!!!! Thank you!!!!!!!!!!” tweeted Olivia Habinck, president of the College and Young Democrats of Iowa.