Donald Trump's attack on Democrat Hillary Clinton's faith isn't the first time he's questioned whether his rivals are true believers,
NBC News notes.
When retired neurosurgeon Ben Carson began besting Trump in the GOP polls in October, Trump went after Carson, popular with evangelical voters. Carson is a member of the Seventh-day Adventist church, and Trump at a rally drew a distinction between his own faith and Carson's.
"I'm Presbyterian," Trump said. "Boy, that's down the middle of the road, folks, in all fairness. I mean, Seventh-day Adventist, I don't know about. I just don't know about."
In January, it was Texas Sen. Ted Cruz turn. Cruz, also popular with evangelicals, is a Southern Baptist, and son of a pastor who fled Cuba.
"Just remember this," Trump said at the time. "In all fairness, to the best of my knowledge, not too many evangelicals come out of Cuba, OK?"
Trump also attacked the 2012 nominee Mitt Romney in March after Romney began urging Republican voters to reject Trump.
Trump called Romney a "choke artist" and asked a crowd in Salt Lake City, "Are you sure he's a Mormon?"
Now that he's all but secured the GOP presidential nomination, Trump on Tuesday turned his attack on the Democratic presumptive nominee Hillary Clinton, a lifelong Methodist.
"We don't know anything about Hillary in terms of religion,"
Trump told a group of evangelical leaders in New York City. "Now, she's been in the public eye for years and years, and yet there's nothing out there. There's like nothing out there."
Trump has also taken slaps at President Barack Obama's religion, asking on Twitter after the death of Supreme Court Justice Antonin Scalia in February, "I wonder if President Obama would have attended the funeral of Justice Scalia if it were held in a Mosque? Very sad that he did not go!"