... Democrats realized that they couldn’t bring Republicans to their column just by harping on Duke’s long history of racist and anti-Semitic activity. They had to make a different case, pitched to voters who by and large loathed the Democratic candidate.

So they seized on a traditional election-year argument: a Duke victory would lead to job losses. Edwards’s campaign enlisted David Dixon, a key player in the construction of New Orleans’s Superdome, to argue that the city’s convention business would suffer if Duke won. So would many other industries, the Democrats predicted, because no one would want to invest in a state led by an ex-Klansman.

Democrats continued to hit Duke for his racist past, of course, which helped draw a record turnout from African-American voters. But the key to Edwards’s resounding triumph—and to the repudiation of David Duke—lay in the appeal to white Republicans, who were more worried about Louisiana’s economic health. In exit polls, over two-thirds of Edwards’s supporters named “the economy” as the most important issue in the runoff election.

The lesson for Democrats in 2016 seems clear. In the event of a Clinton-Trump matchup, it may not be enough to underline Trump’s odious personal qualities or his obvious lack of qualifications for the White House. Already, there are concerns that Trump is unique among the Republican candidates in his ability to win crossover votes from culturally conservative blue-collar workers who have traditionally aligned with the Democrats. Democrats will have to take Trump down the wonky way—by showing how his policies would ruin the American economy. But they may also have to admit that Republicans find Clinton odious, persuading GOP voters to cast a ballot for her even as they hold their noses.

Whatever its ugly racial dimensions, Trump’s proposed wall between the United States and Mexico would cost between $400 billion and $600 billion over the next 20 years. His tax-cut plan would lose a whopping $10 trillion in tax revenue during the next decade, even operating on the dubious assumption of much faster economic growth, and would certainly exacerbate income inequality. According to the Committee for a Responsible Federal Budget, Trump’s tax cuts would increase the ratio between federal debt and gross national product by 70 percent. Freezing immigration and starting a trade war with China will also have adverse economic effects. All in all, it’s likely a Trump presidency will plunge the U.S. into a recession. ...