It's natural for an RNC chief to want his party unified in support of its presidential candidate. But it's not clear that Priebus's threat is helping his party. If Donald Trump wins the election, then it is unlikely that Kasich or Bush will run in four years.
If he loses, on the other hand, Priebus or his successor at the RNC will have two interests that both cut against making good on his threat. Republicans will want to tamp down the intraparty recriminations that would follow the defeat. This is, after all, part of what promoting party unity means. Republicans will also want to win back the voters who deserted them because of Trump. Trying to punish prominent Republicans who shared these voters' anti-Trump sentiments would set back that goal.
Even now, making the threat does not appear to be enhancing Republican unity. Kasich aides told Priebus to buzz off. Ted Cruz endorsed Trump, but nobody thinks it was because he feared the Republican National Committee.
But it's not just Trump-supporting Republicans who are making foolish threats of punishing the Republicans with whom they disagree. Writing in USA Today, Gabriel Schoenfeld says that anti-Trump conservatives should "banish" everyone from the Republican Party who has endorsed Trump, including House Speaker Paul Ryan. Max Boot, an adviser to past Republican presidential candidates, Schoenfeld speaks for him and many other #neverTrump types.
Getting rid of everyone who endorsed Trump is an ambitious goal, given that most of the party's elected officials fall into that category. It's even more ambitious when you consider that the reason so many of them endorsed him is that most Republican voters support him: 87 percent of them in one recent poll. No ambitious Republican politician, even one as solidly anti-Trump as Nebraska Senator Ben Sasse, is going to repudiate all those voters.
So there would be too many people to purge, and too few people interested in doing it, for Schoenfeld's plan to succeed. It would not even have the full support of the small faction of the party that is still dead-set against Trump. Some Republicans find Trump too odious to support but respect other Republicans' reasons for reaching a different conclusion. Some of them don't think punishing Trump supporters is practical. Some of them, like leading #NeverTrumper Bill Kristol, of purges.
How would the strategy be executed, anyway? House Republicans are not going to dump Ryan as their leader because he endorsed Trump: Most of them endorsed the nominee, too. Primary voters in Ryan's district aren't going to vote him out because he endorsed Trump: They voted in large numbers to renominate him after he did it, and the opposition he faced tended to come from people who were more pro-Trump than he is.
None of that means that anti-Trump Republicans should give up on influencing their party. But a realistic strategy would have to set limited objectives. In the event of a big Trump defeat, his critics should have no qualms about arguing that nominating him threw away a winnable race and that people who played key roles in enabling his nomination, like Sarah Palin and Jeff Sessions, made a costly error of judgment that should make people less willing to follow their lead in the future. In that way and others they should work to reduce the influence of the Trump faction within the party.
But that wouldn't mean casting Palin or Sessions into outer darkness. And it doesn't -- can't -- entail repudiating the voter who picked Trump in the New Hampshire primary because he seemed like a successful and entertaining businessman. Or the South Carolinian who thought he was the only candidate who took his concerns about illegal immigration seriously. Or the politician who decided after Trump won the nomination that he is preferable to Hillary Clinton.
What anti-Trump Republicans need to do, in other words, is patiently tug the party in a better direction. For people with strong anti-Trump views -- views with which I sympathize! -- that course is bound to be less emotionally satisfying than calling for purges. Perhaps the pro-Trump and anti-Trump Republicans have more in common than they realize: Both seem intent on pursuing their grievances rather than their interests.