When tomorrow’s first Democratic presidential debate was scheduled, it was viewed by the Hillary Clinton camp as more of a formality to be endured on the way to her coronation than a genuine test of her candidacy. None of Clinton’s potential challengers was taken seriously and she was seen as not so much the frontrunner as the inevitable nominee. But a year of gaffes, scandals, and a generally incompetent campaign has brought Clinton down to earth. So has the unexpected surge of Bernie Sanders. Sanders is leading in New Hampshire and is competitive elsewhere. With Vice President Joe Biden pondering jumping into the race, the forum to be aired on CNN has assumed the kind of importance that the Republican debates have in that competitive race. But while those hoping for the kind of donnybrook that has characterized the GOP standoffs are probably going to be disappointed, the stakes couldn’t be higher. Whereas initially the debate was a meaningless exercise that could not possibly affect the outcome of the Democratic race, now Clinton is under considerable pressure. Though she remains ahead in all the national polls, Clinton must now approach tomorrow evening as if her candidacy depends on it. Any other result but a clear Clinton victory and especially an outcome that is perceived as a defeat or a win for Sanders or one of the others present such as Martin O’Malley in the Democratic debate will likely trigger Biden’s entry in the race and place Clinton’s presidential hopes in jeopardy.

Clinton’s supporters are trying to sound confident and they have reason to do so. The former secretary of state is no fool and has already gone through the ordeal of debating an opponent in 2008 that was far stronger than any of her current rivals. After enduring Barack Obama, Bernie Sanders and the likes of O’Malley, James Webb, and Lincoln Chafee shouldn’t intimidate Clinton. A practiced debater, she’s likely to stay on message and to be able to ignore tough questions about her shifting positions or her Clinton Foundation conflict of interests or lies about emails, should any be posed to her by the moderators.

But the precipitous decline in her fortunes and the rise of Sanders puts her in a position where any slip-up on her part is going to be magnified into a major disaster. Similarly, the expectations for her competitors are so low that if any one of them stand out and give a particularly strong performance when compared to Clinton, it will be viewed as a fatal sign of weakness just at the moment when that is the last thing she needs.

This debate could be the moment when Clinton starts to reverse her fortunes and re-establishes her position as the dominant frontrunner. A clear win in the debate or an evening in which none of the others — especially Sanders — is thought to have done well will do that. That would discourage Biden as well as assuring Clinton’s donors that now is not the time to jump ship in search for a reasonable alternative to the socialist senator from Vermont.

But if there is any signature moment in this debate where Sanders or the others snapping at Clinton’s heels are able to corner her and illustrate the unprincipled nature of her quest for the presidency will be a catastrophe for her. So, too, would be a major gaffe or slip-up that illustrates the gap between her husband’s formidable political skills and her diminished appeal to voters.

Clinton may be comforted by the thought that Sanders seems to have no interest in attacking her because he thinks such tactics are beneath him. But the more combative O’Malley and Webb may have no such inhibitions. Registering little support in the polls, they also have little to lose by throwing caution to the winds and pressing Clinton to explain her hard tack to the left for the primaries. The small field, in comparison to the chorus line of candidates at the GOP debates, also makes it easier for one of them to stand out while also putting pressure on Clinton to be on her toes the entire program.

But as in the rest of the campaign, Clinton’s biggest problem is not her opposition but herself. Running largely against her own record as a relative moderate in an increasingly leftist party, Clinton’s turnabout on the trade bill is widely seen as an expression of her deep cynicism. If the nomination is slipping from her grasp, it is because she is viewed as fundamentally dishonest. That’s bad in any year but in a time when voters in both parties are searching for alternatives to a failing establishment, it is a huge problem.

In that sense, Clinton holds her fate in her own hands. If she does well, she can put to rest the notion that she is about to implode and return the Democratic race to being a boring contest with only one possible outcome. But a few misplaced barbs or dismal attempts at humor or if she falters under attack will have the opposite effect. If Clinton loses the debate, it will set in motion a series of events like Biden’s entry that could spell the eventual end to her campaign.