But a look at the trajectory of Mr. Paul’s career shows that he and his closest political allies either wittingly or unwittingly courted disaffected white voters with extreme views as they sought to forge a movement from the nether region of American politics, where the far right and the far left sometimes converge.

In May, Mr. Paul reiterated in an interview with Chris Matthews of MSNBC that he would not have voted for the Civil Rights Act of 1964 outlawing segregation. He said that he supported its intent, but that parts of it violated his longstanding belief that government should not dictate how property owners behave. He has been featured in videos of the John Birch Society, which campaigned against the Civil Rights Act, warning, for instance, that the United Nations threatens American sovereignty.

In the mid-1990s, between his two stints as a Texas congressman, Mr. Paul produced a newsletter called The Ron Paul Survival Report, which only months before the Oklahoma City bombings encouraged militias to seek out and expel federal agents in their midst. That edition was titled “Why Militias Scare the Striped Pants Off Big Government.”

An earlier edition of another newsletter he produced, The Ron Paul Political Report, concluded that the need for citizens to arm themselves was only natural, given carjackings by “urban youth who play whites like pianos.” The report, with no byline but written in the first person, said: “I’ve urged everyone in my family to know how to use a gun in self-defense. For the animals are coming.”

Mike Holmes, former editor of The American Libertarian, who has known Mr. Paul from libertarian circles since the 1970s, contended that the newsletters did not “rise to the level of hate speech.” He added: “It goes more to the level of social commentary. There was no use of any ‘N’-words. It amounted to the style of foul-mouthed punks trying to get inside the gang of paleoconservatives.”

Those newsletters have drawn new scrutiny through Mr. Paul’s two recent presidential campaigns. The New Republic posted several of them online in 2008 and again recently, including a lament about “The Disappearing White Majority.” The conservative Weekly Standard ran an article highlighting the newsletters last week.