Washington (CNN) Donald Trump revived questions of President Barack Obama's religion on Wednesday, saying the President went to a mosque in Baltimore because "maybe he feels comfortable there."

"I think that we can go to lots of places. I don't know, maybe he feels comfortable there," Trump told Fox News' Greta Van Susteren. "We have a lot of problems in this country, Greta. There are a lot of places he can go and he chose a mosque. I saw that just a little while ago. So that's his decision, it's fine."

Before he questioned Ted Cruz's eligibility for the White House , Trump spent more than a year stoking "birther" questions about Obama's birth certificate and whether he was a Muslim.

Obama, who is a Christian, mocked Trump at the 2011 White House Correspondent's Dinner , saying that Trump probably thinks the U.S. government also faked the moon landing and rattled off other conspiracy theories.

Trump largely dropped his effort after Obama produced his birth certificate, which showed he was born in Hawaii. But Trump has continued to attract controversy on questions surrounding Obama and his background.

And during a speech to the Republican Jewish Coalition in December, shortly after the San Bernardino terrorist attack, he questioned why Obama refused to use the term "radical Islamic terrorism."