Bush's position — "I guess" included — perfectly summarizes where Republicans stand on marriage equality today. They may oppose gay and lesbian couples' right to wed, but they've largely passed the issue over to the courts as judges have struck down states' marriage bans and the public's support for same-sex marriages has strengthened.
Some Republican officials — see Idaho Gov. Butch Otter — continue making noise about their opposition. But most in the party seem content abandoning the issues altogether. They may not support same-sex marriage, but they're not going to fight it. Marriage equality rarely came up in the 2014 midterm elections.
The truth is there's really not much Republican officials could do. Since the US Supreme Court struck down the federal ban on same-sex marriages, federal and state courts have been nearly unanimous in their position that states' same-sex marriage bans violate the US Constitution. Short of a federal constitutional amendment or US Supreme Court decision reversing those rulings, marriage equality increasingly looks like the law of the land.