Republican U.S. presidential candidate Dr. Ben Carson said Sunday he “absolutely would not agree” with having a Muslim as the American president. Carson’s comment on NBC News’ “Meet the Press” television program came on the heels of his GOP competitor Donald Trump’s failure to correct an audience member who alleged President Barack Obama was both a Muslim and a foreigner Thursday. “We have a problem in this country, it’s called Muslims,” the audience member said. “Our current president is one. We know he’s not even an American.”

Answering questions about faith and the presidency, Carson said: “I would not advocate that we put a Muslim in charge of this nation. I absolutely would not agree with that.” The retired neurosurgeon said it was important that a president’s faith be consistent with American values. “If it’s inconsistent with the values and principles of America, then of course it should matter,” he said.

Carson said he believed Islam was incompatible with the U.S. Constitution. When asked whether he would vote for a Muslim for Congress, the presidential contender said he would have to evaluate the hypothetical candidate’s policies. There are more than 3 million practicing Muslims in the U.S.

Asked whether he believes Obama is a Christian who was born in the U.S., Carson replied he had “no reason to doubt” that Obama was a U.S.-born Christian.

In contrast, Trump has focused on Obama’s birthplace in the past, joining members of the so-called Birther movement who alleged Obama was born in Kenya, his father’s home country. Meanwhile, when Trump previously appeared on “Meet the Press,” he deflected a question about the possibility of a Muslim becoming president by answering: “Would I be comfortable? I don’t know if we have to address it right now.”

Carson also addressed foreign-policy issues during his interview. Assuming he were elected president, he said he would do everything possible to fight the Islamic State group. He said he would hope to drive the militant group out of Iraq and into Syria where it would fight the regime of Syrian President Bashar Assad. “Let them fight each other,” he said.

Carson and Trump led the pack of Republican candidates in several recent opinion polls.