Nobody knows where Donald Trump will stand six months from now in the bizarre Republican presidential campaign. But you can predict with some confidence how his recent anti-Muslim diatribes will look in a decade or two, unless Trump manages to rewrite the Constitution. 

American politics, like most things, is a story of what statisticians describe as the reversion to the mean. Self-proclaimed saviors and other outliers come and go throughout our political history. Occasionally they’re successful; most times, they’re not. But the system has rebalanced toward the basic principles of tolerance, freedom and democracy that were set forth by the Founders....

Trump’s anti-Muslim rhetoric will live in infamy in U.S. history. He obviously doesn’t mind; his narcissistic personality is so extreme that every high-visibility outrage is for him a kind of validation. (If you’re curious about other examples of such personalities, read the recent book “Narcissism and Politics: Dreams of Glory,” by Jerrold Post, the CIA’s former director of psychological profiling.)

But the judgment of history should matter to other Republicans. Historians will look harshly on those who, for reasons of cowardice or opportunism, kept silent when Trump’s tirades put our constitutional values and the safety of Americans at risk — not to mention the political future of the GOP.

House Speaker Paul D. Ryan (R-Wis.) offered the simplest and most direct rebuttal Tuesday, the day after Trump called for a ban on Muslims entering the United States: “This is not conservatism. What was proposed yesterday is not what this party stands for, and more importantly, it’s not what this country stands for. Not only are there many Muslims serving in our armed forces dying for this country, there are Muslims serving right here in the House, working every day to uphold and to defend the Constitution.”

Ryan gets my “Have You No Sense Of Decency, Sir?” award, named for the famous rejoinder by Boston lawyer Joseph Welch, who called out the reckless anti-communist crusader Sen. Joseph McCarthy in the 1954 Army-McCarthy hearings. Those seven words began the reversion to the mean after the Red Scare.

People will play the Ryan video clip decades from now when they want to understand when the United States began to regain its balance....