As Donald Trump marches toward the Republican nomination, many people have taken to comparing the GOP front-runner to Adolf Hitler. But prominent white supremacist David Duke says these comparisons are backfiring and could actually be “rehabilitating” Hitler’s image.

“They might be rehabilitating that fellow with the mustache back there in Germany,” Duke said on his radio show, Right Wing Watch reported Wednesday. Duke, a former leader of the Ku Klux Klan, said he saw a “really vicious commercial” against Trump but that he did not think it was having the intended effect.

The commercial, he said, compared “what Donald Trump said about preserving America and making America great again to Hitler in Germany preserving Germany and making Germany great again and free again and not beholden to these Communists on one side, politically who were trying to destroy their land and their freedom, and the Jewish capitalists on the other, who were ripping off the nation through the banking system.”

It was not clear which commercial Duke was referring to, but there have been videos released recently that compare Trump to the infamous German dictator. One ad, released by a group called Citizen Super PAC, features clips of Trump and Hitler speaking and includes the Republican saying America “doesn’t win anymore” as well as Hitler mentioning “the decline of our nationhood.” The video also shows both men criticizing “negotiators” and “deals.”

Trump has had the support of Duke and other white supremacists since he entered the presidential race over the summer. Duke previously called Trump’s candidacy a “great thing,” and last month, he told his listeners that voting against Trump would be “treason to your heritage.”

When CNN asked Trump if he would denounce the endorsements of Duke and groups like the KKK, Trump avoided the question by saying he needed to learn more. After he was quickly attacked by Democrats and Republicans, Trump disavowed Duke and blamed his comments on a “very bad earpiece.”

Duke — and other white supremacists — have kept up their support, despite Trump’s rejection.

“This war that’s going on against Donald Trump is really a war going on against America. It’s a war going on against the European-American majority,” Duke said on his radio show this week, mentioning a euphemism white supremacists use to describe white people. “If you’re a European person, the government is purposefully wiping you out and your families and your children and your future. They are purposefully transforming this country into a Third World nation.”