Trump during the December debate. (Robyn Beck/AFP/Getty Images)

The evolution* of the mainstream Republican reaction to Donald Trump has gone something like this. First, the idea was that Trump would stay mired at 4 percent or so, so no big deal. When Trump took the lead, the thinking was that his lead would fade. When it didn't fade, the idea was that, as the field narrowed, Republicans would consolidate around a more mainstream opponent. (Full disclosure: A lot of pundits went through the same evolution.)

The field hasn't narrowed. Trump still leads, with Ted Cruz nipping at his heels in Iowa. The "how Trump loses" arguments have splintered, assuming that he'll stumble after New Hampshire or that he'll implode if he loses Iowa or that ____________ (please use your imagination). Part of the reasoning for a Trump collapse over the long term has been that there are so many Republicans that simply refuse to ever vote for him. How can a guy win the nomination if a big chunk of the party wouldn't support him?

In the new Washington Post-ABC News poll out this week, nearly a third of Republicans say that he's "unacceptable" as the party's nominee.

So surely he's doomed, right? Well, no — and for two reasons.

Trump isn't even the least-acceptable option

That 32 percent of Republicans who say that Trump is unacceptable? That's actually lower than some of his competitors.

By contrast, 38 percent say that Chris Christie is unacceptable, and 45 percent — nearly half! — say that of Jeb Bush. Trump is polarizing; 81 percent of Republicans in our poll either found him unacceptable or had him as their first or second choice. Forty-nine percent of Republicans pick Trump as their first or second choice — nearly equal to the number that find one-time establishment favorite Bush unacceptable for the nomination.

What's more, 65 percent of Republicans thinks a Trump nomination would be acceptable — essentially tied with Cruz and the now-establishment-favorite Marco Rubio.

At one point, it looked like Trump was never going to be able to get a majority of Republican voters if the race reduced to two candidates. That's simply no longer the case.

The anti-Trump vote is splintered

We can dive into those numbers to see what the anti-Trump vote looks like. Among that 32 percent of the party that thinks he'd be unacceptable as the nominee, support is fragmented all over the place. A fifth of those voters back Rubio. Fifteen percent back Cruz. Thirteen percent back Bush.

In other words, the group that vehemently dislikes Trump doesn't have a preferred alternative. Nearly 30 percent like another of the outsider candidates; everyone else likes one of the also-rans or one of the establishment favorites. Bringing that group of voters together to vote for one candidate to stop Trump seems ... unlikely.

So how does Trump lose at this point? Well, we'll see what happens once voting starts. The last resort of every campaign — the one thing that can stymie all the pundits and bigwigs in the world — is people actually casting votes. We haven't quite gotten there yet.

* These are the mainstream guys. They're okay with evolution.