DES MOINES, Iowa (AP) — Rougher shoving and sharper jabs are expected as a tighter field of Democrats takes the stage for Tuesday night’s final debate before Iowa’s leadoff presidential caucuses.

Just six candidates are gathering in Des Moines, all anxious for a televised boost before the Feb. 3 caucuses that could give one or more of them momentum for the primaries that will then come hot and heavy. Or the Iowa results could all but end their White House hopes.

State polling shows Iowans’ preferences too close to call.

Some of the fiercest clashes could center on Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts, fellow progressives who until now have largely avoided criticizing each other.

Warren chastised Sanders over the weekend following a report that his campaign instructed volunteers to speak poorly of her to win over undecided voters. The tensions escalated on Monday after CNN reported Sanders told Warren in a private 2018 meeting that he didn’t think a woman could win the election, a charge that Sanders vigorously denied but that Warren said was true.

The feuding will likely expand to include nearly every candidate on stage. Sanders has recently stepped up his attacks on former Vice President Joe Biden over his past support of the Iraq War, broad free-trade agreements and entitlement reform, among other issues. Minnesota Sen. Amy Klobuchar, who has had several strong debates, will be looking for another opportunity to highlight her candidacy as she remains mired in the middle of the pack in polling. Billionaire Tom Steyer will have to answer criticism that he’s trying to buy his way to the White House.

And with two surveys showing Pete Buttigieg losing support in Iowa, the former mayor of South Bend, Indiana, will need a breakout moment to regain strength before the caucuses.

Those shifting dynamics mean Tuesday’s debate could be unlike any of the others that came before it this cycle. The generally polite disputes over policy items including health care and immigration are about to be replaced by increasingly bitter and personal knocks. And it will happen as many Democratic voters are just beginning to tune into the race.

“The debates are always important — but this one’s probably the most important for these candidates,” said Scott Brennan, a former Iowa Democratic Party chair and current committeeman. “We’ve got at least four people who are bunched right there together at the top. So how do you break out?”

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Not to be forgotten amid the focus on the Democratic race, President Donald Trump’s reelection campaign announced it would fly a banner in the skies over Des Moines for several hours before the debate. Trump himself was countering by hosting a campaign rally in Milwaukee.

The debate, on the campus of Drake University and televised on CNN, marks the first forum with an all-white lineup. Businessman Andrew Yang, an Asian American candidate who appeared in the December debate, failed to hit the polling threshold for Tuesday’s event. And New Jersey Sen. Cory Booker ended his campaign on Monday after he didn’t make the debate stage, leaving just one black candidate — former Massachusetts Gov. Deval Patrick — in the race.

This will be the first debate since Trump authorized the killing of Iranian Gen. Qassem Soleimani, which heightened tensions throughout the Middle East.

Biden advisers see that development as a boon to his candidacy, allowing him to argue he’s a steady, experienced alternative to Trump. But it could easily become a problem if Biden fails to answer what will likely be pointed attacks from Sanders on his support for the Iraq War.

While Biden acknowledged over a decade ago his vote was a mistake, he’s struggled to offer a clear answer for his support, at times misleadingly asserting that he opposed the war from the start.

Sanders is eager to take the fight to Biden, as his advisers believe his message on income inequality and major structural change can appeal to the same white working-class voters who make up much of Biden’s base.

While Sanders and Warren have, until this weekend, publicly defended each other on the debate stage and in media interviews, Sanders’ team is expecting attacks from the Massachusetts senator on the debate stage. They believe that the Warren campaign is responsible for leaking what they say is an inaccurate description of their 2018 private meeting, as reported by CNN. But in a statement later Monday, Warren said the description of their meeting was correct.

“Among the topics that came up was what would happen if Democrats nominated a female candidate. I thought a woman could win; he disagreed,” Warren said in a statement. “I have no interest in discussing this private meeting any further because Bernie and I have far more in common than our differences on punditry.”

The clashes could offer an opportunity for candidates who stay above the fray. While Klobuchar sparred with Buttigieg during the last debate, she’s previously sought to tamp down tensions among her opponents and avoided taking moderators’ bait to go after other candidates.

And Steyer, who has largely flown under the radar throughout the campaign, could look to capitalize on a handful of recent polls that have shown him gaining traction in some of the early primary states.