Last night he was engaged in damage control after it emerged that he once employed an undocumented housekeeper and failed to pay her social security taxes.
Under pressure from the press, Mr Wilson admitted he and his former wife employed the Mexican woman while he was mayor of San Diego 16 years ago - although he insisted he knew nothing about her illegal status until last month. It was not against federal law to hire illegal labour until 1986, but state law banned knowingly hiring someone without documentation - although this was widely ignored as the Golden State's economy relies on low-paid illegal Hispanic labour.
During his successful campaign for re-election as California's Governor last year, Mr Wilson exploited the anti-immigrant mood by strongly supporting Proposition 187 - laws passed by referendum banning illegal immigrants in California from receiving health care, education and other benefits.
Yesterday, as accusations of hypocrisy began to fly, it was too soon to say whether the "scandalette" would hamper his presidential chances in the long term. But it will not ease the business of raising the many millions he will need for his outsider's bid.
"Nannygates" have claimed several major political scalps, notably Zoe Baird, whose nomination as US Attorney General collapsed after it emerged that she had broken the law by employing illegal domestic staff.