Ever since Donald Trump flubbed a question about former Ku Klux Klan Grand Wizard David Duke, pundits have wondered whether Duke’s support will hurt Trump at the polls. But looking back at Duke’s own electoral history, perhaps we should be asking a different question: Can the Democrats lure GOP voters to defeat a rogue Republican?

That’s what happened in Louisiana’s “Race from Hell” in 1991, when Duke ran for governor. And it just might provide a game plan for Hillary Clinton to defeat Trump in November, if she plays her cards right.

Back in 1991, Duke finished second to Democrat Edwin Edwards in the state’s multiparty primary. In the ensuing run-off between Duke and Edwards, GOP incumbent Buddy Roemer—the third-place finisher in the primary—endorsed Edwards, not Duke.

More importantly, so did three-quarters of Roemer’s supporters, who were heavily Republican. Many of them detested Edwards, who had faced multiple allegations of corruption and would eventually serve eight years in jail for bribery and extortion. Indeed, six of ten people who voted for Roemer thought that Edwards was a “crook.”

But the vast majority of them voted for Edwards anyway, swayed by the campaign’s most famous bumper sticker: “Vote for the Crook. It’s Important.” Designed by a Roemer supporter who feared a Duke victory, the sticker became so popular that Edwards affixed one to his own car.