...In all seriousness walking away from the table from a centrist is the only leverage the far left has in electoral politics, and I can't shake the suspicion that pledging to remove it from consideration is something like unilateral disarmament. It's not about purity, it's about getting results eight, twenty years down the road.
Republicans get this, which is why their far right wing has more clout in the party. For all the excoriation of Nader voters post-2000, there's been no left-wing third party candidacy as successful as Perot or Buchanan. The margin of victory in Florida was 500 votes; any number of things, most notably improved turnout could have swayed it one way or the other, but Perot really did sink Bush's bid for re-election, and the Republicans were much less nasty to his supporters than dems are to the Bernie or Busters. And now that the party has offered up a candidate that's unacceptable to conservative ideologues, business interests, and neoconservatives, there's a horde of NeverTrumpers that are willing to sacrifice a single election to tell the party that their Jacksonian wing can die in a fire, even if it means electing someone as loathsome as Clinton.
Romney might endorse Johnson FFS. And like, this election is the Republican's to lose; it's a tossup on the fundamentals, but the Democrats decided to nominate someone with
worse favorability ratings than Walter Mondale or Barry goddamn Goldwater. But if Clinton does get elected, the Republicans are going to put the blame squarely where it belongs: on a nominee that was unacceptable to wide swathes of the electorate. One can hope that the Republicans won't make the same mistake again. And that the Democrats won't, either.