Republican leaders laid out a blueprint for the revival of their party after the defeat of Mitt Romney in the 2012 presidential race. “If Hispanics think we do not want them here, they will close their ears to our policies,” the so-called autopsy report warned, noting that Mr. Romney had received 27 percent of the Latino vote, down from George W. Bush’s 44 percent in 2004. Quoting Dick Armey, the former House Republican leader from Texas, the report cautioned, “You can’t call someone ugly and expect them to go to the prom with you.”

Yet now, Republicans are doing just that. Donald Trump has emerged as the party’s standard-bearer while scapegoating Latinos and other minorities to stoke the fears and resentment of working-class white voters. Mr. Trump insists he will win Latino votes, yet he began his campaign by promising to build a wall along the border with Mexico to block out the people Mexico is “sending” to the United States, claiming: “They’re bringing crime. They’re rapists.” He recently created another wave of consternation by accusing an American-born federal judge of being biased because of his Mexican ancestry.

The Trump candidacy has put other Republican candidates in a bind. They can tie their lot to his immigrant-bashing campaign and hope that voter-suppression tactics will blunt the growing segments of the electorate galvanized by the prospect of defeating him. Or they can disavow him, recognizing that further alienating nonwhite voters will do severe damage to the party in the long run.

Besides being self-defeating, vilifying groups of people is morally abhorrent. Republicans are signaling to millions of citizens and aspiring Americans: You’re not welcome here; this is not your home.