Sen. Rand Paul (R-Ky.) is standing by an aide who, for years, made pro-secession and pro-Confederate arguments.
There has been no evidence of discriminatory behavior by aide Jack Hunter, Paul said.
"All I can say is, we have a zero tolerance policy for anybody who displays discriminatory behavior or belief in discriminating against people based on the color of their skin, their religion, their sexual orientation, anything like that," Paul said. "We won't tolerate any of that, and I've seen no evidence of that."
Paul's comments follow a report from the conservative Washington Free Beacon about Hunter, who joined Paul's office as social media director in 2012. Hunter worked with Paul on the 2011 book The Tea Party Goes to Washington.
In his 20s, Hunter was the chairman of the League of the South, a group that "advocates the secession and subsequent independence of the Southern State from this forced union and the formation of a Southern republic," according to the Free Beacon report.
Anti-Defamation League Investigative Research Director Mark Pitcavage called the group "implicitly racist."
During his radio career, Hunter also discussed "racial pride" and expressed his support for the assassination of President Abraham Lincoln, according to the Free Beacon. In 2004, Hunter wrote that the Lincoln assassin John Wilkes Booth's heart was "in the right place."
During his time as a radio host, Hunter would also make public appearances wearing a mask with the Confederate flag printed on it. Paul brushed off the mask when asked about it.
"It was a shock radio job. He was doing wet T-shirt contests. But can a guy not have a youth and stuff? People try to say I smoked pot one time, and I wasn't fit for office," Paul said.
Paul added that he had been "vaguely" aware of Hunter's past work, adding that if he had known more, he still would have hired Hunter.
"I think it's hard," Paul said. "The thing is, I grapple with this. What am I supposed to do? I'm going to have a lot of people working for me. They've all got writings and opinions.