But then something funny happened. When his legislative agenda stalled and his ballot measures failed, Schwarzenegger reversed course. The new Schwarzenegger compromised with Democrats on the budget, raising taxes and funding new public infrastructure. He abandoned his opposition to gay marriage, passed redistricting reform, and enacted cutting-edge legislation to reduce greenhouse-gas emissions. He proposed sweeping health-care reform based on Mitt Romney’s successful Massachusetts plan. It failed, but when President Obama passed a national health-care law (also based on Romney’s plan), Schwarzenegger defied furious Republicans and eagerly hopped aboard, which enabled his state to roll out its Obamacare exchange smoothly. By the end of his tenure, it was impossible to deny that Schwarzenegger had become a highly effective governor.

The reasons for this bear directly on a hypothetical Trump presidency. Schwarzenegger’s loyalty to Republican doctrine was tissue-thin. He joined the GOP because he vaguely shared its veneration of wealth and success. But his sub-intellectualism, which initially made him so repellent, turned out to be an asset. When conventional Republican governance made him unpopular, he had no incentive to go down with the party ship. The only thing Schwarzenegger really craved was popularity. Running for office as an exercise in ego gratification may not be as good a thing as running as a serious candidate with good ideas, but it’s much better than running as a serious candidate with bad ideas.

Having left Sacramento five years ago, Schwarzenegger floats around Trump’s candidacy like a half-forgotten doppel­gänger. When Trump left Celebrity Apprentice to launch his campaign, Schwarzenegger took over as host. He appears in ads for the video game Mobile Strike as a joyfully hawkish ­general — barking, “Send a dozen choppers, when one chopper would do” — which have aired in heavy rotation during Republican debates. The juxtaposition has an understated hilarity. Video-game pitchman Schwarzenegger, like Trump, sounds like a parody of the foreign-policy thought offered by the actual GOP candidates, who promise to bring back torture and make the sand glow. The difference: Schwarzenegger, like Trump, is only playing a character. The truly dangerous Republicans are the ones who believe their own dialogue.