U.S. Senate candidate Tom Campbell's support of same-sex marriages came under attack 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.