Sen. Rand Paul (R., Ky.) knew that one of his closest aides had worked for years as a neo-Confederate radio host known as the "Southern Avenger" and hired him anyway, according to a new book about the Republican presidential contenders.

Paul also fought to keep the aide, Jack Hunter, on his staff for two weeks after the Washington Free Beacon first reported that Hunter had spent over a decade working as a pro-secessionist shock jock in South Carolina.

The July 2013 report set off a media firestorm over Hunter’s radio commentary, which included criticism of Mexicans, support for the Confederacy, and praise for the assassination of Abraham Lincoln.

However, behind the scenes Paul fought against advisers who counseled him to cut Hunter loose, according to McKay Coppins’s The Wilderness: Deep Inside the Republican Party’s Combative, Contentious, Chaotic Quest to Take Back the White House.

Hunter, who renounced most of his radio commentary in a July 2013 interview with the Free Beacon, resigned nearly two weeks after the story broke.

"L’affaire Hunter left many in the political world perplexed by why it had taken Rand so long to do what obviously needed to be done, and why he seemed to be taking it all so personally," reported Coppins. "But inside Rand World, the reason was obvious. Hunter wasn’t just any run-of-the-mill secessionist political aide: he was a friend of the family."

"The truth was that Rand had known all about Hunter’s Southern Avenger alter ego," wrote Coppins. "[I]t had just never occurred to him that a radical resume should preclude a talented operative from joining his team."

Paul also didn’t want to "give the neocons the satisfaction of a scalp" by cutting ties with the aide, according to Coppins. But his initial decision to stand by Hunter alarmed advisers, including political consultant Trygve Olson.

"Olson called up [Paul’s chief of staff] Doug Stafford in Rand’s office and told him what every political operative in Washington already knew: You guys have to fire Hunter," wrote Coppins.

"Stafford replied that it wasn’t going to happen. Rand had made up his mind; he thought the Free Beacon story was a cheap shot, and he didn’t want to give the neocons the satisfaction of a scalp. Besides, he didn’t think it was ultimately that big of a deal."

Only after Olson met with Paul and made the case that Hunter would be damaging to Paul’s presidential aspirations did the senator relent.

"Yeah he probably has to move on," Paul told Olson, according to the book. "But I don’t want to fire him."

"Olson assured Rand that he wouldn’t have to, that they would persuade Hunter to quietly slink away on his own," wrote Coppins. "Rand signed off on the decision, and finally, almost two weeks after the Free Beacon story went live, Hunter resigned."

Hunter had a close relationship with the Paul family, as the Free Beacon reported in 2013. He had previously worked for Rand Paul’s father, former congressman Ron Paul, as a campaign blogger. Hunter also co-wrote Rand Paul’s 2011 book, The Tea Party Goes to Washington.

According to Coppins, the Southern Avenger controversy contributed to a growing rift between Rand Paul and his father: a feud that would eventually "derail" the younger Paul’s political ambitions.

"Hunter had come under attack at a time when the relationship between Rand and his dad was growing more fraught with tension and resentment by the day," wrote Coppins.

"And while both Pauls publicly slapped down even the faintest suggestion of acrimony, the truth was that their father-son rivalry had been simmering for years."

The Wilderness covers the run-up to the 2016 Republican presidential primary race and is based on over 300 interviews conducted by Coppins, a senior political writer at BuzzFeed. It was released on Dec. 1.