Donald Trump speaks during a rally in Wilkes-Barre, Pa. (Dominick Reuter/Agence France-Presse via Getty Images)

WITH DONALD Trump’s polling numbers in a tailspin, he has doubled down in calling on Republican vigilantes to take matters into their own hands to thwart what many of them are primed to regard, without proof, as a rigged election. The Republican nominee’s rhetoric, inciting white rural and suburban voters who fear the voting clout of black urban Democrats, is a recipe for voter intimidation and even violence on Election Day. It also lays the groundwork for his followers to believe, if he loses,that his defeat was a historic swindle.

Starting in August, and accelerating this month, Mr. Trump has stood before rallies attended overwhelmingly by his white backers and urged them to go to “certain areas” on Election Day. “Go and vote and then go check out areas because a lot of bad things happen,” he said in Pennsylvania, where lax state laws allow poll watchers to challenge voters as they arrive at precincts. “You know what I’m talking about,” he added. On Monday, he told his followers that they must watch “other communities.” “I hear these horror shows, and we have to make sure that this election is not stolen from us and is not taken away from us,” he said. “And everybody knows what I’m talking about.”

Yes, everyone knows what Mr. Trump is “talking about.” Mr. Trump’s odious gambit is a punch to the gut of American democracy that all but ensures charges of Election Day fraud, no matter how flimsy the evidence. It’s also in keeping with long-standing voter-suppression schemes in state legislatures, where white Republican lawmakers have used the concocted threat of voter fraud as an excuse to enact voter ID laws whose main purpose is to disqualify and discourage minority voters, who disproportionately lack the required documents.

This Republican project is racially intentional, as a recent federal court ruling in North Carolina said explicitly. It dovetails with other, similarly racist tactics in other states, such as the disenfranchisement of felons long after they have completed their sentences — a rule that has left 1 in 5 black adults ineligible to vote in Virginia.

Elsewhere, GOP vote suppression is even more transparently hostile to mass and minority turnout. In Florida, Republican Gov. Rick Scott last week refused to extend the deadline for voter registration even as Hurricane Matthew menaced his state, disrupting a surge in 11th-hour registrations. Mr. Scott, chair of a pro-Trump super PAC, said Floridians had had plenty of time already to register. U.S. District Judge Mark Walker disagreed, ordering the deadline extended on his authority Monday and expressing contempt for what he called the governor’s “wholly irrational” decision. He added: “This case is about the right of aspiring eligible voters to register and to have their votes counted. Nothing could be more fundamental to our democracy.”

Republican presidential candidate Donald Trump told supporters at a rally in Dimondale, Mich., Aug. 19, "No group in America has been more harmed by Hillary Clinton's policies than African Americans." (The Washington Post)

That’s exactly right. And it should pose a basic question for Republican leaders, including House Speaker Paul D. Ryan (Wis.) and Senate Majority Leader Mitch McConnell (Ky.), as they contemplate a post-Trump future. Will the GOP embrace the novel idea of attracting more voters to its side, or will it continue trying to win elections by discouraging people from exercising their right to vote?