What happens if Donald Trump is the Republican nominee for President?

I'm starting to wonder how the anti-Trump Republicans will react if Trump becomes the Republican nominee for President. The National Review devoted an entire issue to denouncing him, and now Max Boot, in Commentary Magazine, writes that Donald Trump Has No Regard for the Truth.

Donald Trump, the undoubted Republican front-runner after winning the New Hampshire and South Carolina primaries, is — there is no way to sugarcoat this — a liar, an ignoramus, and a moral abomination. I have never previously described any presidential candidates in such harsh terms — not even close — but there is no other way to accurately describe him. There simply isn’t. This past week, the week culminating in his big South Carolina win, provided yet more evidence, as if any were needed, of the validity of all these words to describe him.

Boot continues:

Trump’s ignorance was revealed yet again this past week with his bizarre praise of General John J. Pershing whose supposed example he cited as a model in the war on terror. Here is what Trump said: 

“General Pershing was a rough guy, He caught 50 terrorists who did tremendous damage…and he took the 50 terrorists and he took 50 men and dipped 50 bullets in pig’s blood. You heard about that? He took 50 bullets and dipped them in pig’s blood [which is considered haram]. And he has his men load up their rifles and he lined up the 50 people and they shot 49 of those people. And the 50th person, he said, you go back to your people and you tell them what happened. And for 25 years there wasn’t a problem. We’ve got to start getting tough and we’ve got to start being vigilant and we’ve got to start using our heads or we’re not gonna have a country, folks.”

There’s only one problem with Trump’s inspirational tale: There is no evidence it ever happened. Snopes.com describes this as a common urban legend. It is actually far removed from the way that Captain Pershing dealt with the Moros, the Muslims in the Philippines, in the early years of the 20th century. As I wrote in my book The Savage Wars of Peace: Small Wars and the Rise of American Power, “Captain Pershing preferred to win over the Moros with outstretched hand rather than mailed fist. So successful was his campaign that he was made a datto, or chieftain.” 

In other words, Pershing’s approach was the very opposite of what Trump claimed. Although Pershing was not afraid to use force if necessary, he understood that the Moros could not simply be terrorized into acquiescence to American rule and that excessive brutality could backfire. 

It is offensive that Trump is praising Pershing for war crimes he didn’t commit and simply gobsmacking that Trump thinks that Pershing could have ended the Moro insurrection for 25 years simply by executing 49 prisoners. In fact, while Pershing did help to quell the Moro uprising using a balanced counterinsurgency approach, it never truly ended; the Muslim insurrection in the Philippines continues to this day, a fact of which Trump is undoubtedly unaware.

What will Boot do if Trump is nominated? Will he hold his nose and vote for him simply because he's a Republican? Will he vote for the Democrat as the lesser of two evils? (Seems more likely if Hillary is the nominee). Or will he simply abstain from voting for president?