NASHVILLE, Tenn. -- Until now, Fred Thompson has escaped any serious controversy but recent drug accusations reach to the top of his presidential campaign.

According to the Washington Post, Thompson's campaign co-chairman Philip Martin pleaded guilty to selling 11 pounds of marijuana in 1979 and then pleaded no contest to charges of trafficking cocaine, bookmaking and conspiracy in 1983.

Thompson said the old crimes are an unfortunate result of campaign dirt digging.

"Phil, I'm sure, knows that he should have told me about this. But, he thought it was over and done with and forgotten about," said Thompson. "But, of course, nothing is ever over and done with and forgotten about in this business."

Martin has been one of Thompson's closest aides in the campaign -- even giving the candidate use of his personal plane to travel back and forth to campaign events.

Thompson said he has known Martin for more than 20 years and said that he's a changed man.

"I know him to be a good man, I know him to be a man who's rehabilitated himself and led a productive life. He's my friend, he's going to remain my friend," said Thompson.

Martin served probation for all of the charges and did not serve time in prison.