Wade Spees/The Post And Courier via AP

“We are in a strange place,” Republican Sen. Bob Corker said today. “It’s almost, it’s becoming a cultish thing, isn’t it? It’s not a good place for any party to end up with a cult-like situation as it relates to a president that happens to be of, purportedly, of the same party.”

People like Corker or his colleague Jeff Flake — both of whom opted to retire when faced with at least the possibility that their occasional criticisms of President Trump could subject them to a successful primary challenge from a Trump loyalist — have come to believe that their party has been twisted into a cult of personality. But the truth is that what we’re seeing now is just a new manifestation of forces and tendencies that have been present in the GOP for some time.

Yesterday’s primaries produced at least one surprising result, as Rep. Mark Sanford of South Carolina was defeated by Katie Arrington, who had made Sanford’s insufficient loyalty to Trump a campaign issue. At 4:12 pm on primary day, Trump endorsed Arrington via a tweet, saying that “Mark Sanford has been very unhelpful to me in my campaign to MAGA. He is MIA and nothing but trouble.” In her victory speech, Arrington declared that “We are the party of President Donald J. Trump” (the mark of the most fervent Trump loyalists is that for some reason when speaking the president’s name they reverentially use his middle initial).

But the truth is that Mark Sanford has been perfectly helpful to Trump, if you were judging by his support for the president’s policies. He voted with the president 73 percent of the time, according to 538.com, which is solid if not perfect. The problem, though, is that from the beginning he has been willing to criticize Trump for things like his rampant dishonesty. Arrington made that the centerpiece of her campaign. “Mark Sanford has made it his career to use taxpayer dollars to go on CNN and criticize the president,” she said at one point. That will not stand, and he had to be purged.

Some people have used measures of vote alignment, like Corker’s 86 percent agreement with Trump and Flake’s 85 percent agreement — to charge that these politicians are hypocrites or cowards, who will offer some meek reproach of the president but not stand up to him when it counts. That criticism is misconceived, however, because there’s nothing particularly Trumpian about the legislation they vote on. Agreeing with Trump on a bill just means you’re voting for some Republican priority, one which Trump probably knows barely anything about. These are all conservative Republicans, so of course they’re going to vote for most of that legislation.

Republican primary voters don’t really care about how their representatives voted, because the measure of fealty to the cause has shifted. A few years ago, it was how vigorous you were in opposing Barack Obama. Did you support shutting down the government? Was your criticism of him sufficiently angry and personal? If a policy issue came up in those contests, it was likely to be immigration, which was really about tribal loyalty. If you weren’t devoted enough to keeping out foreigners (especially the non-white ones), then you could lose your seat, as House Majority Leader Eric Cantor found out in 2014.

All it took was a few successful primary challenges, like the ones that ousted Cantor, Sen. Bob Bennett of Utah (in 2010) or Sen. Richard Lugar of Indiana (in 2012), to get the message across to incumbents. That was an important reason why the wall of opposition to Obama remained so unbroken: It wasn’t just a strategy to achieve Republicans’ collective goals; it was also, each of them knew, a way to avoid trouble from the right.

This year, two incumbent Republicans have lost primaries: Rep. Robert Pittenger of North Carolina and now Sanford. A third, Rep. Martha Roby of Alabama, who in 2016 called for Trump to leave the race after the “Access Hollywood” tape came out, has been forced into a runoff she could well lose. Dating back to 2010, these races all show a similar pattern. A seemingly safe incumbent gets a challenge from a hard-right candidate claiming they aren’t faithful to the One True Cause. At first everyone assumes the incumbent will have no trouble fending it off. But then the challenge turns out to be stronger than anyone realized and the incumbent loses.

Democrats have had the occasional successful primary challenge from the left, and may have one or two this year. But the fact that Republican races are being defined by which candidate can claim the greatest loyalty to Donald Trump shows that this isn’t a phenomenon of opposition, in which the out-party’s voters respond to their exile from power by seeking ideological purity. It’s a phenomenon of the GOP. They do it when they’re out of power, and they do it when they’re in power.

It’s hard to say exactly how this would manifest itself if there were an ordinary Republican sitting in the Oval Office right now. But this president not only promotes but demands a cult of personality, and his supporters are responding. What matters to him is much less where you stand than whether you display the proper level of devotion, praising his masterful decision-making, lauding his keen mind, and marveling at his gigantic hands. Do all that and the Republican base won’t turn on you.

But if you stray, you’ll find yourself the next target in the endless search for apostates to purge. It’s important to remember that, having cut taxes but being (rationally) terrified to carry out the vivisection of the safety net they fantasize about, Republicans have virtually no legislative agenda left. What gives the party meaning now is Trump, and little else. When Bob Corker says “It’s almost, it’s becoming a cultish thing, isn’t it?”, the only thing he has wrong is the “almost.”