"I think that's a disgrace, to again question whether or not the president of the United States was born in this country or whether he's a Christian," the Vermont senator said on " CBS This Morning ."

"I thought we were beyond that. It is an outrage," he added.

Trump caught flak Thursday night after not addressing claims by a pair of supporters at a rally in New Hampshire that stated "Obama is a Muslim" and "he's not even an American."

Donald Trump not denouncing false statements about POTUS & hateful rhetoric about Muslims is disturbing, & just plain wrong. Cut it out. -H — Hillary Clinton (@HillaryClinton) September 18, 2015





"All he heard was a question about training camps," Lewandowski said. "The media want to make this an issue about Obama, but it's about him waging a war on Christianity." Corey Lewandowski, Trump's campaign manager, told CNN after the event that the businessman did not hear the portion about Obama being a Muslim."All he heard was a question about training camps," Lewandowski said. "The media want to make this an issue about Obama, but it's about him waging a war on Christianity."

The celebrity real estate tycoon has spent years questioning whether Obama was born in the U.S., saying as recently as July in an interview with CNN he doesn't know where the president was born.

Sanders on Friday decried "this mythology and ugliness" of questioning that Obama was not born in Hawaii in 1961, acknowledging when Sen. John McCain (R-Ariz.) once corrected a supporter during his own bid for the White House.

"We all remember, Trump was one of the leaders of this effort a year ago. I thought maybe he had learned something from that. This is not what American politics should be about," Sanders said.

Sanders also put out a tweet calling on Trump to apologize: