SACRAMENTO, Calif. (AP) – U.S. Senate candidate Tom Campbell’s support of same-sex marriages came under attack last Monday in a statewide television ad funded by a national group that promotes traditional marriage.

Like Democratic incumbent Barbara Boxer, Campbell opposed Proposition 8, the 2008 ballot initiative that banned gay marriage in California.

The 30-second commercials are funded by the National Organization for Marriage, which has been a leading opponent of legalizing same-sex marriages in California and other states. The organization most recently filed friend-of-the-court briefs opposing a federal challenge to California’s same-sex marriage ban.

Brian Brown, executive director of the Washington, D.C.-based organization, said the ads running in Republican-leaning areas of California are designed to undermine Campbell’s support. A Field Poll released in January found Campbell leading the three-way Republican primary, although many voters were undecided.

“I think that once people realize just how liberal Campbell is, his support will wither in the polls,” Brown said. “The more people know how similar his views are to Barbara Boxer, the less likely they are to vote for him.”

Brown said the group hopes to run similar ads until the June primary.

Campbell campaign spokesman James Fisfis said Campbell has made no secret that he opposed Proposition 8.

Campbell believes that people should be allowed to marry whether they’re gay or straight, he said.

He said single-issue voters opposed to gay marriages are likely to support one of Campbell’s Republican opponents, former Hewlett Packard chief executive Carly Fiorina or state Assemblyman Chuck DeVore. Both believe marriage should be between a man and a woman, their campaigns said Monday.

But most voters seem more concerned with creating jobs and controlling federal spending, Fisfis said.

“Those are the focal points, and that’s what we’re campaigning on,” he said. “He’s running for the U.S. Senate specifically to tackle the economic and financial issues facing the country.”

The new ad also links Campbell to Boxer in their support for tax increases, an area where Fisfis said the two “are just worlds apart.”

“On the tax issue, they’re just flat wrong,” he said. “Tom Campbell has nothing in common with Barbara Boxer.”