A post-debate confrontation between progressive senators Elizabeth Warren and Bernie Sanders capped the final Democratic debate before the Iowa caucuses after an evening of infighting on foreign policy, healthcare and what makes a candidate most fit to defeat Donald Trump.

In a sign of the depth of the tension between Sanders and Warren, at the end of the debate, as candidates were shaking hands, the Massachusetts senator walked over to the Vermont senator. Sanders outstretched his hand; Warren did not. It was not immediately clear what the two said but after a few short, apparently stern words from both sides they shook their heads and walked in opposite directions.

The moment came after several days of tension between the two camps, shattering a longstanding detente between America’s two leading progressives. The squabble culminated in a dispute over remarks Warren claimed Sanders had made to her privately about the ability of a woman to successfully take on Trump.

About 45 minutes into the debate, the issue came up and Sanders repeated the denial that he had ever said a woman could not win the 2020 presidential election. Sanders said “as a matter of fact, I didn’t say” that, adding that it was “incomprehensible” he would hold such a view.

Sanders went on to note that he supported Hillary Clinton in 2016 and thought she could beat Trump. When Warren was asked to respond, she earned a loud cheer from the audience by saying only the women on the stage had won every election they ran in.

“Look at the men on this stage,” Warren said. “Collectively, they have lost 10 elections. The only people on this stage who have won every single election that they’ve been in are the women. Amy and me,” referring to the Minnesota senator Amy Klobuchar.

Then things got pettier. Sanders noted that he beat a popular Republican 30 years ago, causing Warren to pause. She said in the last 30 years, and that particular election was 30 years ago, Sanders noted. Sanders was referring to his fight for a congressional seat against Republican Peter Smith.

Though the clash between the two progressive heavyweights had been eagerly awaited, Warren also signaled she wanted to move beyond it. “Bernie is my friend, and I’m not here to fight with Bernie,” she said, though those sentiments were not echoed in the apparently hostile post-debate confrontation.

Other divisions were also on display. Sanders was also ready to get into it with former vice-president Joe Biden. And all the contenders were eager to talk about healthcare. Six were on the stage: Sanders, Warren, Biden, Klobuchar, former South Bend mayor Pete Buttigieg, and businessman Tom Steyer.

The debate began with a wide-ranging discussion on foreign policy, including the war in Iraq and whether to leave some American troops in the Middle East or pull them out. Some divisions were on display. Biden defended his vote on the Iraq war, for which he has been criticized for recently. Sanders contrasted himself with Biden.

“I did everything I could to prevent that war. Joe saw it differently,” Sanders said.

Warren said she supported pulling American troops out of the region. Buttigieg did not give a clear answer on whether to recall all troops or not.

This video has been removed. This could be because it launched early, our rights have expired, there was a legal issue, or for another reason. Elizabeth Warren rebukes Bernie Sanders: 'A woman can win the presidency' – video

Later on, ideological divides emerged. Buttigieg became defensive on healthcare, pushing back on criticism that his healthcare proposal was too modest. Healthcare has been a major marker dividing liberal candidates like Warren and Sanders with centrist ones who don’t support Medicare for All: Klobuchar, Biden, and Buttigieg.

“It’s just not true that my plan is small,” Buttigieg said. His plan, called Medicare for All Who Want It, is not as expansive as the Medicare for All proposals championed by Sanders and Warren. “This would be a game-changer.”

Warren was eager to engage with Buttigieg there.

“Look, the numbers that the mayor is offering just don’t add up,” Warren said.

And later on Sanders was asked about the effect his healthcare overhaul plan would have on towns with a large health insurance industry. Sanders digressed.

“We are finally going to have to stand up to the healthcare industry and hundreds of billions of dollars of waste, and profiteering,” Sanders said.

The sense from Democrats on the ground in Iowa ahead of the debate was that despite recent polls showing Biden leading the field, the escalating feuds between Sanders and Warren or Biden and Buttigieg could upend the race.

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“It feels like a free-for-all here,” said Norm Sterzenbach, an Iowa-based Democratic strategist who served as the state director for former representative Beto O’Rourke’s now defunct presidential campaign. Sterzenbach said the primary is full of Democrats not fully committed to one single candidate and he expects an “unprecedented of people are going to walk in on caucus night unsure of where they want to be”.

“These final three weeks are going to have a major impact of who walks out of Iowa. The debates are an important piece of it,” Sterzenbach added.

Candidates will need to differentiate themselves in order to gain ground in the state, said Grant Woodard, an Iowa-based Democratic strategist and former chief of staff to an Iowa Democratic member of Congress.

There’s also a sense that Biden is not impervious and a win in Iowa or a strong debate showing from a rival could oust him from the frontrunner spot.

“There are still so many variables, even till Iowa, that things could change,” said Bradley Tusk, a political strategist who served as campaign manager for Michael Bloomberg’s 2009 mayoral re-election bid in New York.