It has long been clear that the rise of Donald J. Trump meant the end of the Republican Party as we once knew it.

It has belatedly become clear that his rise may have meant the end of the Democratic Party as we knew it as well.

After three Trump elections, almost every traditional Democratic constituency has swung to the right. In fact, Mr. Trump has made larger gains among Black, Hispanic, Asian American and young voters in his three campaigns since 2016 than he has among white voters without a college degree, according to New York Times estimates. In each case, Mr. Trump fared better than any Republican in decades.

There are, of course, many explanations for Kamala Harris’s defeat. President Biden was deeply unpopular and exited late, she was an imperfect candidate, and ruling parties around the world have struggled to overcome a post-pandemic and post-inflation hangover. The polls offer support for all of these hypotheses, and given the closeness of the election, it’s entirely possible that Democrats could have won under slightly different circumstances.

But there probably wasn’t a realistic case of young and nonwhite voters supporting Ms. Harris at a level the Democrats would have taken for granted just a few years ago. And while the election was still close, this erosion of strength among the party’s core groups has been happening for a long time.