National Republicans were quick to disown the white nationalist, probably feeling the need to do so after Trump himself struggled with denouncing Duke earlier this year. And the former grand wizard of the KKK out there on the campaign trail saying nice things about your party's presidential candidate is far from an ideal situation. Duke has regularly praised Trump during the 2016 campaign.
What would be even worse is if Duke caught on. But could he?
Duke, it should be noted, is something of a political gadfly. He threatens to run -- and runs -- often. He has won only once, but in the early 1990s, he gave the Republican Party a series of headaches when he became the party's de facto nominee for Senate and governor.
As a Democrat, Duke lost two state Senate campaigns in the 1970s and briefly ran for president in 1979. He tried again for president in 1988, where he didn't make much headway. He eventually sought and won the nomination of the Populist Party, defeating none other than colorful Rep. James Traficant (D-Ohio). Duke appeared on the ballot in several states and won about 47,000 votes in the general election -- 0.05 percent of the national popular vote.
He finally won his first election in 1989, after switching to the Republican Party and running in a special election for a state House seat. He took 33 percent of the vote in a crowded open primary and went to a runoff with another Republican, John Treen (Louisiana's primary system is different than other states, in that there are no partisan primaries.) In the runoff, Treen had the backing of none other than then-President George H.W. Bush and former president Ronald Reagan -- for a state House race! -- as well as many top Democrats, but Duke beat him narrowly.
"I can't help but tell you of the high regard I have for one candidate in the race for the 81st district -- John Treen," Reagan said in a radio ad.
Duke went on to serve one term in the statehouse, but spend much of his time there aiming higher. He ran for U.S. Senate in 1990 and did better, taking 43 percent of the vote. Polls had shown Duke running second in the primary, at around 30 percent, and the other GOP candidate's presence on the ballot threatened to throw the race to a runoff -- something Republicans didn't want. So instead,
Duke GOP favorite Ben Bagert dropped out and top Republicans endorsed the Democrat, incumbent Sen. Bennett Johnston Jr., who won a majority and avoided the runoff.
Riding higher after that showing, Duke ran for governor in 1991 and made the runoff with former governor Edwin Edwards (D), but he lost there, 61-39. (This is he race that bore the bumper sticker "Vote for the Crook. It's Important." The "crook," of course, was Edwards.)
He finished fourth in a crowded primary for Senate in 1996, with just 12 percent. He also failed to make a runoff in 1999 in a heavily conservative congressional district.
Duke had his moments in the sun in Louisiana, and as the Bush and Reagan endorsements and the 1991 Senate race gamesmanship show, they were enough to give the Republican Party heartburn. The party also tried to block Duke from even running for its presidential nomination in 1992. (At one point, a young Wisconsin Republican named Scott Walker argued with Duke on TV about whether Duke should be on the ballot.)
And as Duke's 1990 and 1991 campaigns showed, about 4 in 10 Louisianans were willing to vote for the former head of the KKK. Even in losing, Duke made a point about the appeal of his message.
Today, he's very unlikely to get anywhere near that level of support. He is, though, running in a very crowded open primary in which even a limited base of support could register. In the 1996 primary, for example, he took 12 percent, but he was only 10 points from making the runoff.
Right now, there are more than a dozen candidates running for retiring Sen. David Vitter's (R-La.) seat. It's a crowded field featuring two current and one former GOP congressmen; the GOP's standard-bearer in the 2008 Senate race, former state treasurer John Kennedy; a tea party candidate who made some waves in the state's 2014 Senate race, Rob Maness; and as many as two statewide officials, including a Democratic public service commissioner, Foster Campbell.
Unfortunately for Republicans, Louisiana is both a state that has been uniquely welcoming to the message of a candidate like Duke, and also has an electoral process -- an open primary -- that allows for that sort of candidate to make an impact. If Duke is able to co-opt Trump's message for himself -- and he's got competition in that regard, as other GOP Senate candidates are supportive of Trump, too -- he won't have to take much of the vote to register in the polls and make another statement.
Hence, the quick disowning of David Duke on Friday.