The leading Democrat in the U.S. Senate race lamented the growing attention Thursday being paid to his past drug use, while the Republican front-runner warned voters to disregard smear tactics targeting him and his family before Tuesday's primary elections.

"Drugs and divorces. That's what it has turned into. It's very depressing," Democrat Barack Obama (search) told The Associated Press after a talk at DePaul University.

Obama, a state senator, said voters should decide whether past drug use by him or other candidates should be an issue in the race as he offered a more detailed explanation of his past use of marijuana and cocaine, which he first disclosed in his 1995 autobiography.

Meanwhile, GOP front-runner Jack Ryan's (search) campaign acknowledged it was making automated telephone calls to warn potential voters of "an unprecedented smear campaign aimed at Jack Ryan and his family."

Ryan spokeswoman Kelli Phiel denied the calls were related to unsubstantiated allegations from a rival campaign about Ryan's relationship with his former wife, actress Jeri Ryan. The allegations have not been publicized.

Rod McCulloch, manager for John Borling (search), who trails Ryan badly in the seven-person GOP race, claimed the allegations are contained in sealed records from Ryan's divorce and child custody case. He acknowledged that he did not know whether the information was true.

Borling said later Thursday that McCulloch had resigned at his request because he had disobeyed Borling's order not to discuss the matter.

Ryan, a millionaire investment banker, has refused to disclose the contents of the sealed records, saying they relate to the custody of his 9-year-old son. Ryan refused to discuss McCulloch's allegations.

"I've tried very hard to be transparent. I've released my tax returns. I've released my financial assets. I've released my divorce records. The only thing I'm keeping sealed is the stuff surrounding my son," Ryan said Thursday.

The race to fill the seat being vacated by Sen. Peter Fitzgerald is shaping up to be one of the year's most high-profile and expensive campaigns in the battle over who will control the narrowly divided Senate. Democrats consider it a crucial seat if they are to regain the majority.

Obama acknowledged that he used cocaine "a few times" and "primarily smoked pot" in high school and his first two years of college, starting when he was about 16 and ending when he was about 19.

After the DePaul event, Obama said he wrote about his drug use in his book "because I think I was not untypical of young men in that generation, particularly African-American men who I think often engaged in self-destructive behavior — pushing away from education, trying to act cool by embracing unconventional behavior."

Obama said it's up to the media and voters to decide if drug use is a relevant campaign issue.

"I think that, at this stage, my life is an open book, literally and figuratively. And I think voters can make a judgment as to whether dumb things that I did when I was a teenager are relevant to the work that I've done since that time," he said.

The drug issue didn't come up during a Democratic debate Wednesday night, but Obama's opponents were asked about it afterward.

Businessman Blair Hull said he had smoked marijuana and used cocaine "occasionally" but stopped in the early 1980s. State Comptroller Dan Hynes said he had smoked marijuana four times while a college student. Former Chicago school board president Gery Chico said he also smoked marijuana when he was in college. Cook County Treasurer Maria Pappas said she had never used illegal drugs.