When you’re at number one in Iowa and rising fast in New Hampshire, then a giant hammer is headed your way. So viewers of Wednesday’s Democratic debate came prepared to watch a collective pounding of Pete Buttigieg, many in the hopes that he’d stagger off the stage into the arms of a political emergency-care team. But only Tulsi Gabbard took out the knife, and it seems to have done only minor damage, if any. That the mayor of a town half the size of Yonkers can gain such steam, polling about as well as John F. Kerry did around the same time in 2003, tells us something about the troubles facing the Democratic field. A front-runner and an impeachment trial are preventing Democrats from having a thorough look at everyone in the establishment lane, leaving Joe Biden to float limply above the pack, even as his balloon deflates. At this point, Biden’s participation in the race may be one of his party’s biggest problems.

Many Americans on the left are frustrated by the presence of either Bernie Sanders or Elizabeth Warren in the race. Either they feel that Warren is just as good or better and Bernie’s time has passed, or they feel that Bernie is the only true radical and Warren is a fraud. Whatever the case, the Democratic race will offer a robust and well-vetted candidate in the alternative lane—someone who will be the foil to the establishment favorite. That could be Bernie Sanders or Elizabeth Warren—or even Andrew Yang or Tulsi Gabbard. One of these non-establishment candidates might win the nomination in an upset, like Jimmy Carter in 1976 or Barack Obama in 2008. The trouble is that Democrats have yet to field a robust establishment candidate, and Biden’s presence has helped smother the vetting of others in that lane. Most primary voters just don’t know or care a lot about the alternatives. This means they could wake up to the weaknesses of their nominee long after he or she has been chosen.

Every Democrat has his or her vulnerabilities, but Wednesday’s debate only underscored how feeble Biden has become. Listening to him is like watching a young child wobbling without training wheels, except there’s no progress and the stakes are higher. Whether it was a call to address domestic violence by “punching at it and punching it and punching at it” or his claim that he was endorsed by “the only African American woman elected to the U.S. Senate” while sharing a stage with Kamala Harris, Biden sounded out of it and tired. Matters of race or gender almost feel like bad sportsmanship to bring up with him, given that addressing them is like crossing a room full of laser trip wires. But he seems not even to have thought about how to make it through those traps. Donald Trump barrels through them all with a middle finger extended. Elizabeth Warren memorizes the map and climbs through like an A student. But Joe Biden wings it with a random mix of sideways walking and high-stepping and murmuring “oh, dear” as he sets off yet another alarm, causing nothing but faces buried in hands.

In a strange way, Biden’s gaffes work in his favor, because they look like a symptom of honesty. But even a press corps desperate to prevent a Trump reelection will be unable to ignore Biden’s propensity to prevaricate about matters trivial and nontrivial. He has told fake war stories, boasted of nonexistent academic achievements, and copied the words of others as his own. The point isn’t that his untruths are equal to Trump’s. But they’re part of a legion of liabilities that require a compelling reason to tolerate.