And it’s not just any voter fraud. In a subsequent radio interview, he clarified that “other communities” in his Ambridge talk referred to Philadelphia, a majority-minority city. That description wasn’t really necessary, though: Anyone who doesn’t know what that phrase—or “certain areas” or “some other place”—really means has slept through all of American history. In Pennsylvania and Michigan, Trump’s supporters may very well believe they can now besiege, clog, and disrupt minority-area polls for one day, and thus shift the states’ electors to Trump.

These threats come at a fraught moment for voting rights. November 8 will be—as Ari Berman, author of Give Us the Ballot: The Modern Struggle for Voting Rights in America, has pointed out—the first presidential election held since the conservative majority on the Supreme Court gutted the enforcement provisions of the Voting Rights Act. Because of the court’s decision, the U.S. Department of Justice has withdrawn federal election monitors—which it had planned to deploy in 11 states—from all but a few areas. It’s also the first one since the rash of post-2010 Republican-sponsored “voter ID” laws passed; these measures are bound to—indeed, are seemingly designed to—cause confusion, conflict, and litigation under the best of circumstances.

But Trump’s attacks aren’t just threatening to minority voters. Or to the integrity of the political system, which should protect the franchise of all American voters. If put into practice, his calls for election “monitoring” could also open his supporters up to legal action. This election could prove to be the perfect test case for voter-intimidation lawsuits.

Let’s be clear: Every campaign uses volunteer poll watchers, and has a legal right to do so. “It’s very common to have people at the polls,” election-law guru Rick Hasen told The Washington Post. “What’s different is that he is couching it in an incendiary way by saying ‘Crooked Hillary’ wants to steal the election. That seems to be an invitation to go and make trouble.” A poll watcher—I’ve been one—keeps track of who has voted, relays the names to campaign headquarters, and may sometimes report irregularities to election officials or party lawyers. A traditional poll watcher, however, does not directly challenge voters—especially not based on skin color. That is against the law.

Also unacceptable is posing as law-enforcement officers and demanding voters’ IDs, sending out intimidating mailings to minority voters, posting misleading or intimidating signs, or standing at the polls to challenge minority voters’ rights to a ballot. These aren’t hypothetical tactics: Over the past 30 years, the Republican National Committee has been linked to all of these unsavory practices. As part of a long-running lawsuit by the Democratic National Committee, the RNC signed a binding “consent decree” in 1982 promising to stop them. Before the 2012 election, the RNC went to court and claimed that because the United States has an African American president, minority voter suppression is no longer a problem. They also argued that laws like the Help America Vote Act, which is designed to streamline registration and voting, make voter fraud more likely, and thus their so-called “ballot security” programs were needed. The Third Circuit held, however, that the RNC is still bound by its settlement agreement. If the RNC does not violate the agreement this year, it will expire in 2017. If it does, it will be extended for another eight years.