The younger Mr. Black denies being a white supremacist.

“I am a white person who is concerned about discrimination against white people,” he said in an interview at a local Starbucks. And yet, Mr. Black, speaking softly, wearing a black leather hat, boots and a sports coat a size too big, could not identify a single ideological difference with his father or the K.K.K.; nor could he bring himself to agree with the tenet that all men, regardless of race, are equal.

Last month, at a “Euro-American” conference in Tennessee organized by David Duke, one of the nation’s best-known white supremacists, Mr. Black gave a speech comparing his campaign to George C. Wallace’s resistance to desegregation in the 1960s. In an audio recording posted online, Mr. Black can be heard telling the crowd that he sees local Republican politics, “especially with the election of Obama, as the way white people will have to respond.”

“We can infiltrate,” he said, adding, “We could politically take the country back.”

Deborah Lauter, director of the civil rights division of the Anti-Defamation League, said that only a handful of other white extremists had tried (and mostly failed) in the last few years to join mainstream politics. She described them as “stealth candidates,” and Mr. Black acknowledged that his racial views were not a prominent part of his campaign.

In fact, Republican leaders here say they had never heard of him, or his family, until reporters from The Palm Beach Post told them he had won one of the party’s 111 seats in the Aug. 26 election.

Then the game changed. Mr. Duke, who was once married to Mr. Black’s mother, Chloe Hardin Black, appeared in West Palm Beach this month to broadcast a radio show describing Mr. Black as a victim of discrimination.