The boos that rang out in Cleveland’s Quicken Loans Arena on Wednesday, when Ted Cruz studiously avoided endorsing Donald Trump in his convention speech, will echo for years to come—and the Texas senator will come to regret it.

Cruz and his supporters might think that he’s won a moral victory by refusing to kiss Trump’s ring, and holding firm to conservative principles, when he told the crowd, “Stand and speak and vote your conscience.” Indeed, the admiration that Cruz won on Wednesday extends to anti-Trump forces at large who might not have respected him before. The New York Times’ Ross Douthat, who has criticized Cruz for being a cynic, tweeted, “It’s possible that this hurts Cruz in 2020. It’s possible it helps him. Who knows? The future is unwritten. The point is: Keep your honor.” Former Obama speechwriter Jon Favreau also had kind words: “In 2020, Cruz will be the only one able to credibly claim he’s the conscience of the party. Ryan, Rubio, etc. took the cowardly way out.”

In terms of preserving his honor, Cruz did the right thing. Trump, after all, was the man who created the slur “Lyin’ Ted,” who insulted the physical appearance of Cruz’s wife, and who slyly suggested that Cruz’s father was involved in John F. Kennedy’s assassination. How could anyone keep their honor and endorse someone who had done all that?

But in terms of his long-term political ambitions, Cruz made a grievous mistake. Political parties are built on loyalty. You’re supposed to stick with your party-mates whether you disagree with them or not. There is some leeway in breaking ranks if a member is demonstrably corrupt, as Richard Nixon was during Watergate. Aside from such emergency exceptions, though, there’s nothing worse a party member can do than to fail to support a fellow candidate in their moment of need.

Cruz’s cool rejection of Trump calls to mind the crisis that engulfed the Republican Party in 1964, when Barry Goldwater’s nomination polarized the party. Some of Goldwater’s rivals kept a distance, notably Nelson Rockefeller who was roundly booed during the 1964 convention not just for his reluctance to fall in line, but for his criticism of groups like the John Birch Society.

Nixon took a different tack than Rockefeller. Privately, he thought that Goldwater was a disaster for the party. But in public, Nixon was a good soldier. He endorsed Goldwater, and diligently campaigned all over the country, trying to shore of down-ballot candidates threatened by the electoral tidal wave that crushed the Republican Party that year.

Nixon’s loyalty wasn’t forgotten; party members remembered his service. He had many chits to collect when he ran again in 1968 and secured the Republican nomination. Conversely, Rockefeller never lived down his reputation as a traitor and was hated by the conservative wing of the party until the day he died. He never got further than being an unelected vice president.

In 2016, Cruz is playing the role of Rockefeller, and Marco Rubio (among others) is playing the role of Nixon. History suggests that the Nixon gambit is the smart one, since it’s the only way to win the voters who make up the largest bloc of the GOP right now. If Trump goes down to a massive defeat in November, Cruz and other non-endorsers will be blamed for stabbing the nominee in the back. They’ll be seen by party loyalists as the cause of the defeat. And they will have no future in national politics.