Two weeks ago in this space, I wrote, “[Donald] Trump has never touched the 45 percent mark in the general election RCP average throughout the entirety of the campaign, suggesting he’s up against a hard ceiling.”

This assertion of fact produced some guffaws among those who remember that many pundits wrongly assumed such a ceiling existed in the Republican primary. Also, the piece was published just as Trump was registering a convention bounce that brought his RCP average up to 45.7.

Now, it appears Trump did hit his head on that ceiling. As of Sunday, he has tumbled back to 40.5, about where he was before the Republican convention began.

A downward shift by itself is not proof that substantial gains are impossible to realize in the future. Nor is a summer struggle to clear 45 percent proof. In 1976, according to Gallup, Gerald Ford couldn’t cross that threshold from April through September, but had a strong October and nearly caught Jimmy Carter, ending up with 48 percent of the vote.

Al Gore was below 45 in the Gallup poll through the spring and summer of 2000, before breaking through after his mid-August convention and eventually winning the popular vote (just not the presidency.) In 2012, Mitt Romney was stuck between 43 and 46 in the RCP average all year (not counting his convention bounce) until touching 48 in early October and making a race of it.

But there were logical reasons behind those rebounds. Romney’s spike, for instance, came from a strong showing in the first general election debate—and a surprisingly weak performance by President Obama. Al Gore pulled even after he went from being dismissive of Bush to taking him seriously, even to the point of offering his own tax cut for the middle class. Ford benefited from a number of factors, ranging from buyer’s remorse among liberals (Carter lost four of the final 1976 Democratic primaries) to the passage of time between his controversial pardon of Richard Nixon to an odd interview Carter did with Playboy magazine in which he spoke of having “committed adultery in my heart many times.”

Also, all of those candidates were uninspiring yet inoffensive pillars of the establishment. So long as they were campaigning competently, they weren’t at risk of cratering.

To state the obvious, Trump is different.

It’s true that because he didn’t play by the usual rules, he was prematurely counted out. One pollster mused in June 2015 that Trump’s “cap” might be the 11 percent he then registered in New Hampshire. Philip Klein of The Washington Examiner argued last August that “his support seems to have met resistance at around the 25 percent mark.” Then in January, the New York Times’ Ross Douthat said Trump’s “consistent 30 percent” would not be enough to win.

These pundits (myself included) refused to believe what they were seeing. Since mid-July 2015, Trump led in the RCP Republican primary average every day save for one, with numbers that steadily climbed throughout the process. By the time Trump wrapped up the nomination after the Indiana primary, he had won 40 percent of the total popular vote, blowing past those false ceilings.

However, Trump’s general election trajectory is a different story altogether. There is no steady climb. For the last 12 months in trial heats against Hillary Clinton, he’s rattled between 38 and 44. While we should be careful not to put too much stock in polls taken during the afterglow of the Democratic convention, where the race sits today is where it has sat for much of the year.

In other words, what Trump has been doing is not working. It’s not true that the old rules don’t apply to Trump, even though breaking them allowed him win a plurality of the primary vote. Denigrating immigrants and Muslims, punching down against all critics and delivering narcissistic stream-of-consciousness stump speeches is a losing strategy for a presidential election.

Some may be inclined to pinpoint Trump’s attack on the Muslim parents of U.S. soldier killed in Iraq as the singular unforced error now sinking his campaign. But that cruel act is merely the culmination of everything upon which his entire campaign has been premised. And that is a campaign that has never been anywhere near 50 percent.

Does this mean his campaign is already cooked? Uncertainties remain. Can the third-party candidates allow Trump to win with another plurality? So far, the combined Green and Libertarian vote isn’t altering the outcome in national polls, though we have less data to work with at the swing-state level. Will there be more stolen emails leaked to the media? Perhaps, though Clinton survived the last batch.

Most importantly, is it possible for Trump to overhaul his campaign?

One thing is clear. Jeb Bush was correct: Donald Trump is not going to insult his way to the presidency. A campaign based on bashing minority groups cannot win a national election in this country. If he is to prevail, he’s going to have to change, and change dramatically. And there is little evidence he wants to do that or that could do it if he tried.