Disgust with the choice voters are being given between the two Democrats- one a harridan, and the other a fascist with an isolationist foreign policy- a candidate of Romney's stature might actually have an outside chance of winning. He has nothing to lose. I don't think he'd do it any more than Jeb Bush or Lindsey Graham, who also have nothing to lose- and who, like Romney, have publicly said that they will not vote for Donald Trump. But he would have credibility as a potential president that Trump certainly does not have, and that Hillary ought not to have.
I still see somebody like former Oklahoma Senator Tom Coburn or even some non-politician- Kristol himself, in the worst case- as a more likely third party candidate. But any one of the three- Romney, Bush, or Graham- could well actually have an outside chance, considering that for the first time in history we have two presumptive major party nominees each of whom each is viewed negatively by half or more of the electorate. Think about it: at least half of the American electorate can't stand both the presumptive Republican and the presumptive Democratic nominees.
The situation may well deteriorate further if Trump- who after all has nobody running to his right anymore, and may figure that the conservatives who are falling all over themselves to abandon their principles and support him will continue to do so no matter what- shows his true Democratic colors in the Fall campaign. If he's smart, he won't; his minuscule chance of beating Hillary depends on the hemorrhage of support of his candidacy by Republicans not growing worse, which it surely will if he gives free rein to his inner socially liberal, pro-single payer health system, pro-choice real self.
But who- besides Donald Trump- has ever said that Donald Trump is smart?
Caricature by DonkeyHotey