Many people — myself included — thought it would look something like this: Trump says something truly beyond the pale. Media erupts. GOP elites erupt. Republican primary voters receive a strong signal that Trump lacks either the qualities necessary to win the presidency or the temperament necessary to be the president. Voters abandon him in droves.
This theory of Trump's fall is clearly wrong. It fundamentally misunderstands the nature of Trump's appeal. Donald Trump is the candidate willing to say things that are truly beyond the pale. He is the candidate who won't be cowed by the media or political elites. Every time he stands tall against a "politically correct" firestorm — wherein "politically correct" means treating people with some bare modicum of decency and respect — his numbers firm up. Backlash is his brand.
But there's another model of failure. Trump could just ... not win. He could lose the Iowa caucuses. He could fall short in New Hampshire. A loss in any early state might lead to a loss in every state. Losing a presidential primary is often like going bankrupt: It happens slowly, then all at once.
This is basically how Howard Dean lost in 2004. As Andrew Prokop has written, Dean's lead looked a lot like Trump's: It was big in New Hampshire and small in Iowa, it was based on huge crowds and hot-button issues, and it scared party elites.
And then Dean just ... didn't win. He lost Iowa, and then he lost everywhere. No one really knows why Dean collapsed in Iowa. Theories include a vicious air war with Dick Gephardt and last-minute worries among Iowa caucus-goers that Dean couldn't beat Bush. But there was no defining event behind his defeat — the infamous yelp came later. Dean went into Iowa looking likely to win it, and then caucus-goers abandoned him. The single best sentence I've heard on Dean's loss came from his campaign manager, Joe Trippi. "People get more pragmatic the closer they get to an actual vote," he told the Washington Post.
An important thing to know when reading coverage of Trump is that a lot of reporters and politicos believe something like this is going to happen to him. But the prediction is hard to talk through explicitly because it's so maddeningly vague. It's based on nothing save the fact that it happens all the time. It's the Underpants Gnomes theory of Trump's loss. Step 1: Trump leads the polls for month after month. Step 2: ??? Step 3: He loses! Even if you think that's likely, it sounds a bit ridiculous when you say it aloud.
And yet, this kind of loss is common. Candidates lead, and then they don't. Eric Cantor is invincible, and then he's beaten by some unknown academic. Hillary Clinton is a juggernaut, and then she's beaten by Barack Obama. Howard Dean leads everywhere, and then he leads nowhere. Political analysis is a realm of post-hoc storytelling. Something unexpected or unpredictable happens, and then we explain why it was obviously going to happen all along.
But this is, I think, what will happen to Trump. He will lead until he doesn't. His fall will be quick, and it won't obey the apparent rules of his rise. If there is a reason for it, it will fundamentally be, "People get more pragmatic the closer they get to an actual vote." As much as Republicans tell pollsters they think Trump can win the general election, I am skeptical they will truly believe that come Election Day.