Vice President Joe Biden—who as in previous outings interspersed some strong moments with several mushy or head-scratching ones—seemed emphatically life-sized, once again, in the latest debate in Houston.

There is an optical dimension to presidential politics that is hard to explain in logical terms but hard to deny in practical experience: At some point winning candidates seem to grow larger in public projection and their ability to dominate a stage.

Someone starts the campaign as an ordinary politician, desperate for a few extra seconds on camera, and somehow becomes a leader who doesn’t have to beg or contrive cute one-liners to get attention, by virtue of being very visibly the most consequential person in the field.

One conclusion of Thursday night’s debate, over three hours: Those mysterious optics have not kicked in yet. It was a big stage of people who still seem smaller than the position they are seeking.

Biden’s previous uneven performances didn’t dislodge him atop the race, and so caution is justified in predicting bleeding wounds from this one. Even so, discursive answers on substantive issues like deportation of undocumented immigrants and Afghanistan, an oddly dated reference to a “record player,” disrespectful digs and patronizing swipes from rivals, all raise the question: Can he withstand four more months of this before actual Democratic voting begins?

And, if not, a question for his rivals: When will those mysterious optics of power kick in for them?

A smaller field—10 candidates on one night instead of 20 over two—meant that there was no one present who didn’t pass at least some modest threshold of plausibility. And most of the candidates had at least some moments when their voices carried. But there was no one who clearly owned the stage and loomed obviously larger than rivals.

There’s time yet, of course. It was around this period four years ago when Donald Trump changed in perception from a loud novelty candidate to someone who clearly was in command of the GOP race and made much more conventionally credentialed opponents look small on the stage.

It was strong performances at a debate and on the trail in October 2007 that helped Barack Obama overcome a somewhat slow start and establish himself as front-runner Hillary Clinton’s equal in stature in the Democratic contest.

It does not seem likely that the Houston debate will live in memory as such a moment of transformation.

For one thing, it was at times pretty hard work for the audience: three hours is a lot, especially watching people who of necessity are being quite nakedly calculating in their effort to stand out. One good thing about the length, however, was a somewhat more dignified tone: candidates did not have to shout and filibuster and interrupt to snare the spotlight as much as they did at the summer’s two previous sets of two-night debates.

Elizabeth Warren showed the traits that helped drive her surge earlier this year have survived intact to the fall. But her performances tend to flicker. Crisp and impassioned answers on expanding access to health care or curbing access to guns would be followed by long stretches when she seemed to blend into the background.

The durability of the Biden paradox—not so strong to be running away with the race, but strong enough to keep people who could claim his space among moderate, establishment-oriented Democrats from breaking through—was causing some irritation among rival campaigns after the debate. Biden, by these lights, benefits from clearing a bar that should be higher for a front-runner.

“He didn’t fall over,” an adviser to one of his rivals scoffed, calling Biden “the anti-expectation candidate.”

“I think that we are at a tough point right now, because there’s a lot of people concerned about Joe Biden’s ability to carry the ball all the way across the end line without fumbling,” Cory Booker opined on CNN after the debate.

In truth, however, that bar is still pretty low for all 10 people on stage.

Bernie Sanders, a remarkably consistent debater, whose performances generally are to your taste or not depending on your ideology, sounded the same as ever except hoarser, from what seemed to be a bug of some kind. Mayor Pete Buttigieg proved himself just as articulate as on multiple previous occasions—a fluency that the numbers suggest has so far impressed donors more than average Democrats.

Kamala Harris did not school Biden like she did in their first debate encounter, but she did find high notes in continually turning her fire on Trump, who in one caustic line she likened to the man behind the curtain in “The Wizard of Oz,” who turned out to be “a really small dude.” Julián Castro did try to school Biden, though he risked coming off as rude by not-so-subtly (and inaccurately in context) implying that Biden was suffering from senescence: “Are you forgetting already what you said just two minutes ago?”

Beto O’Rourke, like Castro appearing in his native state, won lots of plaudits from fellow candidates for his response to the mass shooting last month in his home city of El Paso, though the praise was in its own way a bit condescending: A clear signal that they no longer view him as a serious threat for the nomination.

Amy Klobuchar, casting her ideological centrism as a natural outflow of her Minnesota upbringing in the center of the country, and Booker, stressing his affinity for the challenges of urban America, both gave among their stronger performances of the campaign—a reminder of why they initially generated such anticipation earlier in the year. Both need a Biden stumble to lift themselves up.

Lastly, entrepreneur Andrew Yang showed he is the novelty candidate who still seems novel, after author and self-help guru Marianne Williamson failed to qualify for the debate.

To highlight his signature economic policy, Yang announced his campaign would give a “freedom dividend” of $1,000 a month to 10 American families who apply through his website. POLITICO politics editor Charles Mahtesian likened this to Willy Wonka’s five golden tickets.

But it was far from the only stagy moment of the evening. Precisely because the candidates are still struggling to make themselves seem large, there was incessant boasting and self-referential answers that invoked the phrase “I’m the only” in ways that often came off as quite tinny.

I’m the only person on the stage who has beaten the National Rifle Association (Biden), the only person to pass a major bipartisan bill under Trump (Booker), the only person to serve on the Senate Homeland Security Committee (Harris), the only person to have voted against all of Trump’s military budgets (Sanders), the only person to be a public school teacher (Warren), the only person to take control of local schools (Booker again), the only black elected state attorney general (Harris again), and so on.

By far, the more appealing references to self—and in general the most compelling windows into personal character and experience—came at the very close of the debate when moderator George Stephanopoulos asked candidates to talk about how they had been shaped by setbacks in their lives.

Several candidates gave heartfelt answers but it was here in the closing moments when Biden succeeded in ways that often fail him in connecting life experience to a larger rationale for his campaign. Speaking of the deaths he has suffered in his family—his first wife and young daughter in 1972, and his adult son Beau in 2015—Biden said,“The way I’ve dealt with it is finding purpose.

“And my purpose is to do what I've always tried to do and stay engaged in public policy,” he added. “And there's a lot of people been through a lot worse than I have who get up every single morning, put their feet one foot in front of another, without the help I had. There are real heroes out there.”