Ms. Cox did not return several requests for comment. In court documents, Mr. Cox denied that the house was purchased to further an affair, stating it was purchased almost a year after the divorce was filed.
The details of Mr. Cox’s alleged affair stand in contrast to the attacks he and allies mounted along the campaign trail. In an interview with KQED in September, Cox took aim at Democratic opponent Gavin Newsom’s past marital conduct. “If you conduct yourself in a way that exposes you to extortion or to blackmail... that’s really hurting the people you’re representing,” Cox said.
Newsom admitted in 2007 to an affair with his appointments secretary, who also was married to his campaign manager. At the time, Newsom was separated from his first wife.
“I had to own it,” Newsom told KQED earlier this month. “I had to take responsibility. I had to be transparent.”
Caroline Heldman, a politics professor at Occidental College, said most voters will forgive personal marital problems. But undecided voters could be turned off by the apparent hypocrisy of the Cox campaign.
“John Cox made this an issue,” Heldman said. “It was foolhardy to go after his competitors’ infidelities when he has this in the closet. It doesn’t seem prudent.”
Cox attacked Newsom about his affair when he introduced himself to voters in a debate for Republican candidates hosted by the San Francisco Chronicle in February.
“I take issue with Mr. Newsom just passing it off as an indiscretion of his and a moral lapse,” Cox said. “It was far, far more than that. It was an endangerment to his position as a leader of this city.”
As the primary election drew closer, a pro-Cox ad released in April targeted both Newsom and another candidate, Democrat Antonio Villaraigosa, for inappropriate relationships.
The ad, paid for by an independent expenditure organization supporting Cox called Restore Our Values, stated, “Newsom and Villaraigosa think the rules shouldn’t apply to them.” The ad continues, “They don’t want punishment. They want a promotion. Californians deserve better. John Cox for Governor.”
While Villaraigosa was married to Corina Villaraigosa, he dated Telemundo television anchor Mirthala Salinas, and acknowledged the relationship in 2007, according to the Los Angeles Times. "I take full responsibility for my actions," Villaraigosa told reporters.
The Cox campaign said they tried to pull the ad from the air — but not because of its content or tone. The campaign filed a cease-and-desist letter objecting to how the sponsors identified who had paid for it. Despite the letter, the ad continued to air for a week across the state on Fox News.
Heldman said Cox clearly benefited. According to an aggregate of polling results during that time, Cox’s popularity increased by 13 percent in that period.
“It was a statewide buy,” Heldman said. “You could see after the ad hit the state, Cox’s numbers went up and ahead of Villaraigosa. It’s quite possible that Cox is still in the running because they attacked Villaraigosa’s infidelity.”
When asked why he’s made his opponents' pasts a focus, Cox replied, “I’ve made some mistakes in my life. But that’s affected my personal life. I wasn’t the mayor of a major city.”
He remained evasive when asked about his own marital record, turning the discussion instead to issues affecting the state.
“I’m focused on affordability,” he said. “I’m focused on building homes. I’m focused on a gas tax.”
Mr. Cox gave that response at a campaign event on Skid Row in Los Angeles this week. He walked away without answering additional questions. His campaign manager wouldn’t address Ms. Cox’s claim that her husband wanted to stay married to her while he continued another relationship.