In today’s Louisiana presidential primary, the biggest drama is in the GOP, where front-runner Donald Trump has prompted many Republicans to complain that an extremist bigot has hijacked their party. Trump’s ascendancy may be the most surprising development of the year, but it’s not unprecedented. Area voters need look no farther than the story of David Duke to see how a racist demagogue can thwart the Republican establishment, rising to the top of a GOP field for high office.

Duke, the former Klansman and Nazi, was back in the news this month after expressing his support for Trump, who drew the rightful ire of critics for what seemed a half-hearted disavowal of Duke’s backing. That controversy is already fading, as it perhaps inevitably must. In Trump World, after all, The Donald’s daily aggressions against basic civility mean that one moral outrage is quickly replaced by another.

But Duke’s brief reappearance in the public eye brought a timely reminder of how the toxic politics of grievance can grow into a movement more driven by passion than principle, more intent on getting even than getting things done.

Because of his checkered past and slim political experience, Duke was given little chance of success when he began his campaign for governor a generation ago. But he deftly drew on the resentments of white, blue-collar voters who felt that their government no longer heard them. He eventually became the state GOP’s gubernatorial standard-bearer, much to the regret of party regulars who grasped much too late the appeal of Duke’s message.

The story of David Duke has obvious parallels with the predicament of the Republicans in this year’s presidential race, as party leaders awaken, in the eleventh hour of primary season, to the distinct possibility that Trump could be their presidential nominee. That would place the party of Lincoln in the hands of a man who has spouted profanity on the stump, demeaned women and minorities, chatted glowingly of Russian despot Vladimir Putin, Tweeted out the pronouncements of Benito Mussolini, spoken approvingly of the bloody Chinese crackdown in Tiananmen Square, and pledged to crack down on his press critics if elected.

GOP primary voters will have to decide for themselves whether they want such man at the top of their ticket. On that question, Duke’s candidacy yielded at least one more lesson. He floundered among general election voters, ushering in a disastrous fourth term for a corrupt Democrat named Edwin Edwards -- exactly what conservative voters didn’t want. Pitting Trump against presumptive Democratic presidential nomineee Hillary Clinton, who has her own legal problems, could make the general election an echo of the 1991 gubernatorial race, in which many voters felt they had to choose between a crackpot and a crook.

Things rarely end well when voters cast a ballot out of anger instead of self-interest. If Duke has reminded us of that this month, then maybe, at long last, he will have performed a genuine public service.