Mr. Romney’s big problem in 2012 wasn’t among Tea Party supporters; it was among evangelicals. Mr. Romney performed significantly better among Tea Party supporters who weren’t evangelical than he did among evangelicals who weren’t Tea Party supporters.

We can speculate about the reasons for Mr. Romney’s weakness: his Mormon faith, his past support for abortion rights or his opponent Rick Santorum’s overtly religious brand of conservatism. It might even be that Romney, who amassed his great wealth in the Northeast, didn’t share the demographic characteristics of many evangelical Christians, like lower income and a residence in the South.

But a successful challenge to Mr. Bush from the right would have to involve winning a lot of these voters, even though they have been Mr. Romney’s biggest weakness. There is no viable anti-establishment coalition that does not include large percentages of evangelical Christians. Mr. Romney — a Northern Mormon with a history of moderate politics — has not been very effective at winning them over.