Donald Trump cares about winning. So it’s been disconcerting to watch him stage a retreat in recent days.

That rare backtrack most likely came after Trump’s poll numbers plunged among women. And while the reason for this downturn wasn’t immediately clear, it may have had something to do with his refusing to dismiss a tawdry story about Ted Cruz published by his friend at the National Enquirer, defending his campaign manager’s rough treatment of a woman reporter, angering everyone who’s ever taken any position on abortion, and generally behaving like a boor.

Flamboyance of this sort is uniquely Trumpian, unlike anything else on the presidential stage. It’s left pundits groping through the historical vault in search of a parallel.

The most common comparison is to Andrew Jackson. It’s easy to see why. Brash, vitriolic, with an outsize sense of self-regard and a burning contempt for the political establishment of his day, Jackson seems at first glance like a proto-Trump. He spent much of his first term immersed in the Petticoat affair, an imbroglio of personal intrigue over the alleged promiscuity of his secretary of war’s wife. You can imagine the easily slighted Trump frittering away his time on a similarly inconsequential issue.

But however combustible Jackson was, he was also deeply serious. He fought valiantly in the War of 1812. He later served as military governor of Florida and returned to the Senate after a prolonged absence. Nearly everything Jackson did from 1817 onwards garnered controversy, and some of it was deeply wrong, but his presidential qualifications were never in doubt. Comparing Trump to Jackson does a disservice to the latter’s deeply complex role in our history.

Another oft-made comparison is to William Jennings Bryan, the former Democratic presidential nominee. Again, there’s a passing resemblance. Bryan’s populism and advocacy for the American interior against its coastal establishments frustrated his party’s leadership. Like Trump, Bryan was scorned by elites, and never so eloquently as when Scopes Monkey Trial lawyer Clarence Darrow labeled him “the idol of all Morondom.”

But Bryan’s big ideas—for Free Silver, against the Spanish-American War — are an intellectual world away from Trump’s proposal for Mexico to fund a wall on its own border. Bryan gave masterful speeches like “Imperialism” and “The Cross of Gold”; Trump rambles about himself. Earlier figures from the Populist Party, like James B. Weaver and Thomas Watson, don’t line up either.

The realization is stirring: in American history, there probably hasn’t been a successful major-party presidential candidate as simultaneously vulgar, reviled, and unqualified as Donald J. Trump. If it nominates Trump, the Republican Party, which allegedly stands for the familiar and traditional, will sever all its moorings and drift into uncharted waters.

The reason this presidential season feels so unprecedented is because it is.

And unprecedented circumstances tend to draw unprecedented outcomes. Third parties aren’t unheard of in American history, but in recent decades power has been mostly limited to Republicans and Democrats. With both major parties’ frontrunners registering approval ratings on par with typhoid fever, could an independent candidate get real traction this year?

Maybe that’s one historical exception we shouldn’t take exception to.