Tom Campbell – the moderate Republican who supports gay marriage – is in the crosshairs of an unlikely political foe: a group of gay Republicans.

Campbell, a former congressman, is vying against former Hewlett-Packard CEO Carly Fiorina and state Assemblyman Chuck DeVore to win the California GOP Senate primary. In a recent Public Policy Institute of California poll, Campbell and Fiorina, who says she believes marriage should remain solely a heterosexual union, are running nearly even.

The National Organization for Marriage (NOM), the nation's most vociferous opponent of gay marriage, is spending $300,000 in the state on ads attacking Campbell for his support of gay marriage. NOM says it can wrench primary votes away from Campbell because the majority of Republicans are unaware that he supports gay marriage

“Voters want politicians with the courage to stand for their values, not the values of San Francisco,” Brian Brown, executive director of NOM, said in a statement. “We know that Californians, especially GOP primary voters, are going to be asking who will be on their side for the tough fights ahead. As ordinary Californians were standing tall for marriage in the face of enormous pressures, harassment and name-calling during the Prop. 8 battle, Tom Campbell was nowhere to be found. Or rather, he was to be found standing hand-in-hand with [Democrat] Barbara Boxer.”

This is NOM's first major outing in California since it led the effort to pass Proposition 8 – California's gay marriage ban – in November of 2008.

Campbell's gay marriage stance, however, has fallen on deaf ears with gay GOP group GOProud, which released a 30-second web ad attacking Campbell on Thursday.

“Tom Campbell has proposed increasing taxes on California families,” a male announcer says.

“Tom Campbell,” he adds, “Wrong on taxes. Wrong for Republicans. Wrong for California.”

While Jimmy LaSalvia, executive director of GOProud, applauds Campbell for his gay marriage support, his beef with the 57-year-old politician is his record on taxes and foreign policy, which he called “abysmal.”

“Prop 8 was and is a state issue and we agree strongly with Rep. Campbell on Prop 8,” LaSalvia told On Top Magazine in an email. “However, the totality of his record on issues of importance to gay conservatives – particularly his record on taxes and foreign policy – is abysmal.”

Campbell must be judged on national issues, not state issues such as California's gay marriage ban, LaSalvia added.

Similarly themed television and radio ads are also in the works.