And this shift was not just a case of white America making deals at black America’s expense and congratulating itself. Blacks as well as whites had a relatively optimistic view of race relations around the turn of the millennium, and that sentiment persisted until Barack Obama’s second term. Racial polarization hardly disappeared, especially in the voting booth, but it was more muted in the George W. Bush era than before or since. And it might have remained muted if the Bush administration had not fallen into a very different error than racism — the error of unbounded moralistic optimism, which after the Iraq disaster and the financial crisis made darker, more culturally pessimistic varieties of conservatism seem like wisdom to many voters on the right.

So without arguing that racism is going to disappear outright from conservative politics after this presidency, the recent historical record at least suggests that another muting could happen, another substantial diminishment of racial polarization, at some point in the post-Trump future. Especially since there is little evidence that Trump himself is making Americans or Republicans more racist, or that his most racially polarizing strategies are actually politically effective: Instead, his main achievement has been to activate latent bigotries rather than expand their influence, and what can be activated can presumably be suppressed.

If you draw lessons from the 1990s and 2000s, that suppression would require more than just the quarantine of overt white supremacists (though it does require that). First, following the pattern of the crime and welfare debates, it would probably require a sense among populist voters that today’s equivalent to those controversies, the debate over the pace of immigration and the security of the southern border, had been addressed in a way that wasn’t just a capitulation to the left or to big business.

Second, it would require a recovery of influence and moral ambition by the Republican Party’s religious conservatives — a group whose elites shaped the Bush presidency’s racially inclusive efforts and whose rank-and-file are still less inclined to white-identity politics than other conservative constituencies, despite their Faustian bargain with Trump.

Third, it would require some clear successes by Democrats in states like Texas and Georgia, where the G.O.P. is currently hanging on to power with thinning white majorities, to prove to Republican politicians that a strategy of voter-ID laws and base turnout really is as foredoomed as optimistic liberals hope.

Finally, it would require imaginative statesmanship by the next generation of Republican leaders, who would be wise to recognize that the Democratic Party’s leftward shift — and particularly the way that white liberals have lately overleapt minorities in their racial pessimism — is an opportunity and not just a threat, because it leaves a potential pan-ethnic center available for a less bunkered and bigoted populist conservatism to claim.

This list of requirements is not small, and there are plenty of reasons to doubt they will be met. The media ecology has changed since the late 1990s in ways that make suppression and quarantine more difficult. Trump himself had the opportunity and the credibility to make a base-satisfying deal on immigration, but that opportunity has passed. Religious conservatism’s compromise with Trumpism may ultimately prove fatal to its influence. The Democrats’ leftward move should inspire entrepreneurship and outreach from Republicans, but it could help sustain the G.O.P.’s own base strategy instead. Many G.O.P. donors prefer a party of white-identity politics and tax cuts to the more economically populist and ethnically diverse alternative. And Trump’s toxic Twitter influence will endure, no doubt, even once his presidency has ended.