The Democratic 2020 presidential candidates will gather once again on Tuesday night to face off in their fourth debate, this time in the perpetual swing state of Ohio.

Twelve of the candidates have qualified to participate, and they will all share one stage – marking the most crowded debate stage of this election cycle so far. But the dynamics of the race have changed since the candidates last met in September, and some of the contenders face the prospect of this being their last debate.

Here are five things to expect in tonight’s debate:

Biden and Ukraine

Joe Biden will be asked about the false corruption charges that Donald Trump has leveled against him. Trump and his allies have accused the former vice-president of using his influence to benefit his son’s business activities in Ukraine, even though those charges have been repeatedly found to be without merit. In a Good Morning America interview that aired today, Biden’s son, Hunter, denied any wrongdoing in his dealings overseas but acknowledged he should have considered the political ramifications of his work. The real question for tonight is whether Biden’s opponents, who have searched for openings to attack the high-polling candidate, will rally around him in the face of Trump’s false claims.

Warren the new frontrunner

Elizabeth Warren will take the stage as a definitive frontrunner. The Massachusetts senator appears to be creeping ahead of Biden in the polls, and her opponents are taking notice. Indiana mayor Pete Buttigieg released an ad hours before the debate contrasting his healthcare plan with Warren’s. Other contenders will probably pursue a similar strategy during the debate. Warren may also be asked to address questions over her story, which was shared at the last debate, about losing her job due to her pregnancy in 1971.

Sanders’ health

Bernie Sanders will make his official return to the campaign trail after suffering a heart attack earlier this month. The Vermont senator has been recuperating in his home state as his campaign faced questions not just about his health, but also about why his aides chose to wait three days before disclosing the seriousness of the episode. The moderators will probably ask the same question tonight.

Impeachment

The prospect of Trump’s impeachment will hang heavily over the event. This is the first Democratic debate since the House speaker, Nancy Pelosi, formally launched the impeachment inquiry late last month. While all of the candidates who will be onstage have voiced support for the inquiry, some have been much more reluctant than others to say they would back Trump’s removal from office. Biden, for example, only explicitly said the president should be impeached last week, while Warren has been vocal about her support since April.

Last chance saloon

Lower-polling candidates face the prospect of not qualifying for the next debate, which could make them desperate to grab the audience’s attention tonight. Eight of tonight’s participants have qualified for the November debate – Biden, Warren, Sanders, Buttigieg, Kamala Harris, Andrew Yang, Cory Booker and Tom Steyer. Four others – Beto O’Rourke, Amy Klobuchar, Tulsi Gabbard and Julián Castro – have not yet met the polling requirement. With 12 candidates on stage, they will probably be fighting to get a word in edgewise in the hope of seeing a polling bump to catapult them to the November debate.

The debate will stream on the websites of CNN and the New York Times, who are hosting the event just outside of Columbus, starting at 8pm ET.