MOBILE, Ala. — Republican presidential candidate Ben Carson likened Syrian refugees to dogs here Thursday, telling reporters that U.S. authorities must be vigilant to screen out the “mad dogs” among them who may seek to do harm.

Carson said Americans should be fearful of a terrorist attack on the homeland because Islamic State terrorists pose “so much greater a threat to us” than al-Qaeda did before and after Sept. 11, 2001.

“They weren’t nearly as developed as they are now,” Carson said of what he termed the “global jihadist movement.” He added that the 2001 attacks “really didn’t require a great deal of sophistication because we were not paying attention, we were not coordinating our efforts. So you didn’t have to be all that great. You had to be able to fly some planes and get a couple of people in here. That’s going to be a lot more difficult now.”

At a news conference between campaign events in Mobile, Carson said it is natural for Americans to be fearful of a terror strike at home.

“If you listen to what ISIS is saying and what the global jihadists are saying, they’re promising that, yes, they are coming here,” Carson said, referring to the Islamic State by another name. “So is it reasonable to be fearful of such a thing? Of course.”

Carson both defended his knowledge of foreign affairs and distanced himself from adviser Duane Clarridge, a former CIA agent who publicly raised doubts about Carson’s intelligence, as well as Carson’s longtime political confidant and business manager, Armstrong Williams.

Discussing the Syrian refugee crisis, Carson said the United States must balance security needs against humanitarian impulses.

“For instance, if there’s a rabid dog running around in your neighborhood, you’re probably not going to assume something good about that dog, and you’re probably going to put your children out of the way,” Carson said. “It doesn’t mean that you hate all dogs by any stretch of the imagination, but you’re putting your intellect into motion.”

Carson added, “We have to have in place screening mechanisms that allow us to determine who the mad dogs are, quite frankly. Who are the people who want to come in here and hurt us and want to destroy us?”

Asked to respond to Democrat Hillary Rodham Clinton’s characterization in a foreign policy speech Thursday that Islam is not America’s adversary, Carson said he agreed to a point.

“But there are aspects of Islam that I would not incorporate into the leadership of this nation. That’s where the difference lies,” Carson said. “That’s why I’ve said I do not believe that someone who is invested in Sharia [law] would be an appropriate leader in America.”

Carson added, “We’re not going to say, ‘Let’s completely change who we are as Americans just so that we can look like good people.’ We have an American culture and we have things that we base our values and principles on, and I, for one, am not willing to give all those things away just so that I can be politically correct.”

Carson faced several questions about his foreign policy advisers, following this week’s New York Times report in which Clarridge described the ways in which Carson is struggling to grasp foreign policy.

“Mr. Clarridge, I appreciate his service as a CIA agent, and he has sat in on two sessions,” Carson said. “Does that make him a senior adviser? I don’t think so. He’s not one of the people that I talk to on a regular basis to get advice.”

Carson said it would be fair to describe Clarridge as “a consultant,” but that “he’s not an adviser.”

Carson said his principal foreign policy adviser is Robert Dees, a former Army major general, and that he also has consulted former secretary of state Henry Kissinger and Robert “Bud” McFarlane, who was former president Ronald Reagan’s national security adviser.

Carson tried to publicly separate himself from Williams, a longtime adviser who appears frequently on television on Carson’s behalf.

“Armstrong is an independent agent,” Carson said. “He happens to be a friend of mine. He has nothing to do with the campaign.”

However, when a reporter asked Carson who he consulted with about his recent op-ed in The Washington Post, the candidate said he sent the column to Williams to edit.