Bernie Sanders faces standing at a podium for three hours after his recent heart attack but some of his rivals for the Democratic nomination for the White House have problems of their own ahead of Tuesday’s debate in Westerville, Ohio.
Former vice president Joe Biden is facing baseless, but persistent, allegations of wrongdoing overseas that could undermine his argument that he is best positioned to defeat the president while Elizabeth Warren is fending off new scrutiny of her biography.
Mr Sanders is recovering from a heart attack that raised questions about his ability to withstand the vigour of a presidential campaign.
A dozen Democratic presidential candidates will meet on Tuesday for the most crowded presidential debate in modern history.
But it is the three leading candidates, Mr Biden, Mr Sanders and Ms Warren, who face the most intense spotlight that could expose glaring liabilities in their quest for the White House.
The debate marks the first time the candidates will meet since the House moved forward with an impeachment inquiry against President Donald Trump.
While they are united on that issue, the debate will again expose a political party struggling to coalesce around a unifying message or messenger with the first primary contest just over three months away.
The event, hosted by CNN and The New York Times, will be held in Ohio, a state that has long helped decide presidential elections but has drifted away from Democrats in recent years.
The White House hopefuls will represent the political and personal diversity that has come to define the Democratic Party of 2019: four women, four people of colour, an openly gay man and an age range that spans four decades.
Mr Sanders, a Vermont senator, will be under pressure to prove he has the physical and mental stamina to stand on a podium for three hours less than two weeks after suffering a heart attack.
Age was already a concern for the 78-year-old even before he was taken to a Nevada hospital earlier this month and had two stents put in to clear a clogged artery in his heart.
Mr Sanders and his allies insist the health scare has only strengthened his commitment to the 2020 contest and his case for his signature health care plan, Medicare For All.
Mr Sanders plans to note, as he has in recent days, that millions of Americans without health insurance could have been forced into bankruptcy, or worse, under the same circumstances.
“I think the debate is going to be a great reassurance to the public.”
The stakes are also high for Ms Warren, Mr Sanders’ ideological ally, who stands on the debate stage for the first time as a front-runner, a status that makes her a top target of rivals in both political parties.
Mr Biden, 76, and others have jabbed her intense focus on detailed liberal policies that may be difficult to implement with a divided Congress.
South Bend, Indiana, Mayor Pete Buttigieg has highlighted the absence of a specific Warren health care plan; she has embraced Mr Sanders’ single-payer plan instead.
Republicans, meanwhile, have raised questions about whether Ms Warren, 70, was actually forced from her teaching job because of a pregnancy nearly a half century ago, a claim that has become a core part of her personal message.
Critics have pointed to past speeches and documents that suggest she left on her own.
The issue is particularly threatening because it is not the first time she has been accused of embellishing her biography.
Ms Warren, a Massachusetts senator, has already apologised for claiming Native American heritage decades ago.
While it showed distant tribal ancestry, it also sparked a rebuke of Ms Warren from some Native Americans for attributing tribal membership to genetics.
“The good news is that most attempts to attack Warren actually make her stronger,” said Adam Green, a Warren supporter and co-founder of the Progressive Change Campaign Committee.
“Questioning whether she got fired for being pregnant ended up increasing her breadth and intensity of support, particularly among women.”
Mr Biden is no stranger to the pressure of front-runner status.
But he enters his fourth debate under the weight of intensifying questions from Mr Trump about his family’s work overseas.
Mr Trump also insists that Mr Biden used his office to protect his son from allegations of wrongdoing.
There is no evidence to any of the claims, and some of Mr Biden’s Democratic rivals have defended him against Mr Trump’s attacks.
But he will almost certainly be asked by the debate moderators to defend himself.
Hunter Biden will participate in a series of interviews on ABC in the hours before the debate.
Joe Biden addressed the situation over the weekend, promising to bar family members from occupying any office within the White House if elected. But he has yet to address Mr Trump’s allegations facing a national debate audience.
How he fares could determine whether he maintains his place atop the crowded field.
Many other candidates, meanwhile, are fighting for their very political survival.
The debate will also feature Mr Buttigieg, California Senator Kamala Harris, New York entrepreneur Andrew Yang, former Texas Representative Beto O’Rourke, Minnesota Senator Amy Klobuchar, New Jersey Senator Cory Booker, former Obama housing chief Julian Castro, billionaire activist Tom Steyer and Hawaii Representative Tulsi Gabbard.
With the Iowa caucuses scheduled for February 3, time is quickly running out for the lower-tier candidates to make a move.
Based on current polling, several would not qualify for the next round of debates.
The risks offer a compelling reason for the struggling White House hopefuls to be more aggressive.
Mr Buttigieg has squabbled with Mr O’Rourke recently over guns, and he signalled over the weekend that he planned to make a sharper distinction between himself and Ms Warren.
Health care emerged as a key contrast among candidates in recent debates and it likely will again, at least according to the 37-year-old mayor, whose plan would give people a choice of whether to join a government-backed health care system or their private insurer.
Speaking to a labour union audience at a presidential candidate forum in Iowa, he warned that some of his competitors, without explicitly naming Ms Warren, would give Americans no choice.
“I’m not pushing Medicare For All whether you want it or not,” Mr Buttigieg said.