Meanwhile, institutions that were seen as outside or sideways to political debate have been enlisted in the culture war. The tabloid industry gave us the apotheosis of Caitlyn Jenner, and ESPN gave her its Arthur Ashe Award. The N.B.A., N.C.A.A. and the A.C.C. — nobody’s idea of progressive forces, usually — are acting as enforcers on behalf of gay and transgender rights. Jock culture remains relatively reactionary, but even the N.F.L. is having its Black Lives Matters moment, thanks to Colin Kaepernick.

For the left, these are clear signs of cultural gains, cultural victory. But the scale and swiftness of those victories have created two distinctive political problems for the Democratic Party.

First, within the liberal tent, they have dramatically raised expectations for just how far left our politics can move, while insulating many liberals from the harsh realities of political disagreement in a sprawling, 300-plus million person republic. Among millennials, especially, there’s a growing constituency for whom right-wing ideas are so alien or triggering, left-wing orthodoxy so pervasive and unquestioned, that supporting a candidate like Hillary Clinton looks like a needless form of compromise.

Thus Clinton’s peculiar predicament. She has moved further left than any modern Democratic nominee, and absorbed the newer left’s Manichaean view of the culture war sufficiently that she finds herself dismissing almost a quarter of the electorate as “irredeemable” before her donors. Yet she still finds herself battling an insurgency on her left flank, and somewhat desperately pitching millennials on her ideological bona fides.

At the same time, outside the liberal tent, the feeling of being suffocated by the left’s cultural dominance is turning voting Republican into an act of cultural rebellion — which may be one reason the Obama years, so good for liberalism in the culture, have seen sharp G.O.P. gains at every level of the country’s government.

This spirit of political-cultural rebellion is obviously crucial to Trump’s act. As James Parker wrote in The Atlantic, he’s occupying “a space in American politics that is uniquely transgressive, volatile, carnivalesque, and (from a certain angle) punk rock.” (The alt-right-ish columnist Steve Sailer made the punk rock analogy as well.) Like the Sex Pistols, Parker suggests, Trump is out to “upend the culture” — but in this case it’s the culture of institutionalized political correctness and John Oliver explaining the news to you, forever.