Ben Carson

Carson, a devout Christian, says a president's faith should matter to voters if it runs counter to the values and principles of America.

Responding to a question during an interview broadcast Sunday on NBC's "Meet the Press," he described the Islamic faith as inconsistent with the Constitution.

"I would not advocate that we put a Muslim in charge of this nation," Carson said. "I absolutely would not agree with that."

In polls in national and early-voting states, Carson is second only to Trump. He recently cast doubt on the real estate mogul's religious faith, questioning his "fear of the Lord," then backed off the comment and would not repeat it.

"You don't hit a person on faith," Trump told hundreds of people at a rally in Boone.

On one side stands billionaire businessman Donald Trump and his allies, on the other are those who oppose him.

A day after Rick Perry, Texas' longest-serving governor, ended his second Republican presidential run with a whimper, Trump marked the shake-up by embracing his role as his party's 2016 bully on Saturday.