The big primary news on Tuesday was the defeat of Republican Congressman Mark Sanford. It’s a good opportunity to repeat one of my favorite themes: how a party’s interpretation of an election matters, whether the interpretation is correct or not.

Why did Sanford lose? Everybody knows: It’s because Sanford has been critical of President Donald Trump. As the Washington Post put it, “Sanford founders in South Carolina after critical tweet from Trump.”

But is that true? I’m pretty confident that Trump’s late-afternoon tweet didn’t make much of a difference, even if it swayed some last-minute voters. There is, however, good reporting indicating that both candidates talked about their support for Trump during the campaign.

It’s worth recalling that Sanford, the former governor of South Carolina, was previously famous for covering up an affair by claiming he was “hiking the Appalachian Trail.” While he had recovered from the scandal to win back his old House seat, as Kyle Kondik notes, he also survived a serious primary challenge in 2016. For what it’s worth, others who paid attention to the contest said he ran a bad campaign.

I’ll add one more piece of perhaps relevant information: South Carolina Republican Governor Henry McMaster, a very strong Trump supporter whom the president had endorsed, fell well short of avoiding a runoff election.

So put it all together and … I have no idea. Perhaps Sanford wins easily if he doesn’t rock the boat; perhaps attacking Trump cost him just enough to lose; perhaps it made little or no difference.

But none of that matters very much. What does matter is what Republican Party actors, especially Republican politicians and campaign professionals, believe about the costs of opposing Trump. And that won’t come down to careful studies; it will be whatever the news media report and what those within the Republican Party network tell each other.

It looks pretty clear that, at least for now, what they’re all telling each other is that taking on the president from within their own party is a suicide mission. They’ll point to Bob Corker and Jeff Flake, who are retiring; they’ll point to Sanford and to Alabama Republican Martha Roby, who may lose her own renomination contest.

As long as Republican politicians and campaign operatives believe that, they will be extremely reluctant to take Trump on, at least in ways that might show up in primary advertising. Even if it’s not actually true that Trump made Sanford lose. Even if there are plenty of counterexamples out there in which Trump failed to sway Republican electorates — such as Roy Moore’s loss in Alabama.

All politicians are paranoid; what matters is what they’re currently paranoid about. Tuesday’s Republican primary in South Carolina makes it more likely than ever that Republican politicians are going to be paranoid about taking on Trump. Even if it makes some of them, and their party in general, more vulnerable in November.

Jonathan Bernstein is a columnist for Bloomberg News.

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