When conservatives start attacking each other's faith, then you know it's on. In today's GOP, candidates define themselves by their religion so they can court evangelical voters so Ben Carson's attack on Trump's faith is a big deal.

In a fascinating twist to the 2016 Republican presidential race, neurosurgeon Dr. Ben Carson essentially threw down the gauntlet Wednesday and asked evangelical Republicans to choose sides by questioning the authenticity of Trump's faith. Speaking to reporters before a large rally here in Anaheim, Carson was asked by a reporter how he was different from Trump.

His answer was short and direct.

"Probably the biggest thing -- I've realized where my success has come from and I don't in anyway deny my faith in God," Carson said.

He explained what he meant by quoting what he said was one of his favorite bible verses.

"By humility and the fear of the Lord are riches and honor and life and that's a very big part of who I am. I don't get that impression with him," Carson said of Trump. "Maybe I'm wrong, but I don't get that."

Carson, who is a Seventh Day Adventist, has made faith a cornerstone of his campaign message. Powered by the backing of evangelicals, Carson is polling highly in Iowa, a state where about half of caucus-goers this winter are expected to be born-again Christians.

I thought this would happen after Trump mentioned that Carson didn't know much about job creation being a doctor and all, but I didn't expect him to play the God card.

It's on now.