When the Americans defeated the British at Yorktown, the surrendering British forces supposedly played “The World Turned Upside Down.”

The song should be on the soundtrack at Donald Trump rallies. The mogul is marching toward the Republican nomination by trampling every single assumption about presidential politics, especially on the GOP side.

Surely no campaign has ever before had a divisive internal fight over whether the candidate should be presidential or not. But that has reportedly been one of the points of contention between new Trump hand Paul Manafort and old Trump hand Corey Lewandowski, the contestants in a high-stakes episode of “Consultant Apprentice.”

Trump is operating on the rather insulting assumption that he can’t act presidential — i.e., with too much dignity — while also attempting to appeal to his Republican voters, and so far he has been proved right. It’s just one of the ways in which he has seemed to understand the party he is seeking to take over better than its longtime loyalists.

It was once thought that a Republican presidential candidate had to pay constant obeisance to Ronald Reagan and hew closely to certain rhetorical tropes and policy truisms. It turns out that the Republican Party — or at least a sizable element of it — isn’t that conservative, and even what were once thought to be the party’s most rigidly ideological guardians in talk radio aren’t really sticklers for conservative doctrine.

It was once thought that any serious presidential candidate had to have political experience and be a committed member of the party he or she sought to lead, or at the very least not openly threaten it. Trump the novice, who re-registered as a Republican only in 2012, has appended the not-so-subtle warning “or else” to his candidacy from the beginning.

It was once thought that you had to organize a campaign operation, run TV ads and raise money. Trump has barely done any of them.

It was once thought that you had to know something and demonstrate it in every setting, or risk seeming amateurish and not up for the job. Trump has blown through this norm.

It was once thought that you had to act with some decorum, display respect for others and yourself, and avoid vulgarity and public displays of anger. Trump has made it his business to do the opposite and, even after reining himself in a little, is still the most outlandish presidential candidate in memory.

We have destroyed manners and chivalry over recent decades — with popular and celebrity culture leading the way — and the left has tried to replace them with political correctness. As a celebrity comfortable in the realms of Howard Stern and the WWE, Trump has little loyalty to the old standards at the same time he (rightly) rejects political correctness. This is a license for unconstrained boorishness.

And it has played well in the party of evangelicals, of social conservatism and of disdain for Hollywood and for elite libertinism. Trump has barely made a pretense of religiosity, and been incredibly overt in his vindictiveness and braggadocio.

Clearly, what a certain segment of conservatives didn’t like about Mitt Romney wasn’t his pedigree as a Northeastern moderate — which he shares with Trump — so much as his decorousness. Peggy Noonan wrote a book on Reagan called “When Character Was King.” The follow-up for our era could be called “When Character Became a Sign of Weakness.”

The old pieties don’t have the hold they once did, but Trump’s celebrity and unsurpassed media skills have also allowed him to get away with things that more conventional candidates never could. At least with Republican voters. Everyone else is another question. If Trump wins the nomination, he has to hope that swing voters are as enamored of belittling nicknames and brash put-downs (“if Hillary were a man …”), and that the traditional rules of how a president acts and represents the country no longer apply. He will need the world to be turned upside down.

Rich Lowry can be reached via e-mail: comments.lowry@nationalreview.com.