Last week's Public Policy Institute of California poll found that Campbell had 23 percent support among likely Republican voters, one point shy of Fiorina, who had 24 percent support. A third candidate in the race, conservative state Assemblyman Chuck DeVore, had 8 percent support.

His neck-and-neck tie with Fiorina is all the more remarkable considering Campbell supports marriage equality and was a vocal opponent against Proposition 8, the measure voters passed in 2008 that overturned the California Supreme Court ruling in favor of same-sex marriage. Should he be nominated by GOP voters in the June 8 primary, it would mark the first time that Republicans have backed a pro-same-sex marriage candidate who is truly competitive in a statewide race.