Certain Democrats trying to cope with President Biden’s continually underwhelming 2024 poll numbers share an article of faith: the ceiling theory.

All Biden needs to do is rally allies who are unenthusiastic about him — particularly young, Black and Hispanic voters — against Donald Trump. The former president’s ceiling, after all, has proved to be low; he didn’t crack 47 percent in either the 2016 or the 2020 election. And Biden has shown he can win a majority of the popular vote.

There is some truth in that. But it overlooks something important that hasn’t gotten much attention: Polls show that Biden’s ceiling actually appears to be lower than Trump’s.

While much has been made of “Never Trump” Republicans, “Never Biden” voters appear to loom even larger — at least for now.

Back in 2020, it was the opposite. Whenever the question was asked, the percentage saying they’d never vote for Trump outpaced the “Never Biden” contingent by double digits.

Often, at least 50 percent of voters said not only that they weren’t voting for Trump, but that there was no chance they would. At most, just 4 in 10 said the same of Biden.

That’s now flipped.

The most recent poll to show this is Monday’s New York Times-Siena College poll of six key swing states: Arizona, Georgia, Michigan, Nevada, Pennsylvania and Wisconsin. Across those states, 46 percent of registered voters said there was no chance they’d vote for Trump, while 52 percent said the same of Biden.

That’s the biggest gap to date, including an earlier Times poll and CNN polling as recently as last month. But even with smaller gaps, every such poll in recent months has shown more “Never Biden” voters than “Never Trump” ones.

And in 3 of 4 such polls since November, it’s been a majority of voters who say they’ll never vote for Biden — just as it was with Trump in 2020.

Some of this is voters warming to the idea of reinstalling Trump as president.

As has been noted, retrospective reviews of Trump’s presidency have been better than they were at virtually any point when he was actually in office — something labeled by his critics as “Trump amnesia.” The CNN poll mentioned above is a case in point. While 55 percent labeled Trump’s presidency a “failure” in its closing days, 55 percent now label it a “success.”

So it’s no surprise the “Never Trump”segment of the electorate has dropped from 50 percent-plus to the mid- to high 40s.

But it’s also true that Biden just doesn’t appear to be a viable option for lots of voters right now — as much as a majority, and certainly many more than in 2020. That same CNN poll showed 61 percent regarded his presidency thus far as a “failure,” for instance.

The high “no chance” numbers for Biden undercut another common strain of perhaps overly optimistic Democratic thought: that the president stands to benefit if and when third-party candidates like Robert F. Kennedy Jr. fade over time (as they often do).

While recent data suggest the Kennedy factor is pulling more from Trump than Biden, some on the left have argued that third-party candidates like him are bad for Biden, full stop. The reason? They lower the threshold for victory for Trump, a candidate who (again) hasn’t proved he can get even 47 percent.

But Trump’s ceiling doesn’t actually appear that low right now; he’s at 49 percent head-to-head with Biden across the six states polled by the Times.

Biden’s ceiling, on the other hand, does appear that low. And that suggests he’s got more work to do than merely rallying the troops against a common enemy.