Bryan Fischer. YouTube/Screenshot Social conservatives are generally horrified by Ohio Republican Sen. Rob Portman's endorsement of same-sex marriage today.

In an email to conservative leaders obtained by Business Insider, conservative Christian radio magnate Rich Bott called the Ohio Senator's gay marriage shift a "betrayal," and suggested that it was further proof that the GOP has abandoned its conservative principles.

"Another Republican establishment figure betrays the party platform and damages the 'brand'," Bott wrote. "Portman was an early Romney supporter and was reportedly on the short list for Romney’s VP selection. What’s wrong with this picture? Lack of good, clear religious/moral teaching for starters."

As Bott's email suggests, the same-sex marriage debate has deepened divisions within the GOP, reigniting old frictions between the conservative Republican base and the party's more moderate Establishment.

But there are indications that the influence of hardline religious conservatives is waning in the GOP, particularly on the marriage issue. While Portman is the only sitting Republican Senator to have endorsed same-sex marriage, other Republican leaders, including top 2016 contenders Marco Rubio and Rand Paul, have started to dodge the gay marriage question, passing it off as a states' rights issue.

And social conservatives aren't happy about that either.

From an email from American Family Association firebrand Bryan Fischer, on Paul's recent statements about gay marriage:

I think Rand Paul’s position on marriage – getting government out of it altogether – is perfectly disastrous. The GOP must not go down this road. Rand Paul does not strike me as a guy who changes his mind much, since he is a man of unbending principle, which is great when he’s right and bad when he’s wrong. He’s just plain wrong on this. If he holds to this position, he must not become the GOP candidate in 2016.