President Trump said in an exclusive interview with Tucker Carlson that he worries withdrawing U.S. troops from Afghanistan could lead to the country again being used as a base to attack the United States.

After the deaths of two U.S. service members last week in Afghanistan, Carlson asked the president how much longer American troops will be deployed there.

Trump, in the interview that aired Monday, said that he has wanted to pull out troops for some time and noted that he has reduced the force "substantially," from 16,000 to 9,000. He expressed his view that the U.S. should avoid being the "policeman for the whole world."

"If you look at Russia, Russia doesn't police the world, they police Russia. You look at China, they don't have troops everywhere, what they have is people taking minerals out of the ground, they don't have troops," said Trump.

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Trump said he "would like to just get out," but the problem is that Afghanistan is a “lab for terrorists.”

"I call it the Harvard of terrorists," Trump said, pointing out that the 9/11 hijackers were trained in Afghanistan with Al Qaeda.

He then described conversations with U.S. generals about his desire to leave Afghanistan, recalling that they emphasized their preference to "attack them over there" rather than deal with attacks on U.S. soil.

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"'Sir, I’d rather attack them over there, then attack them in our land.' That's always a very tough decision with what happened with the World Trade Center. ... It’s something you always have to think about,” Trump said.

Trump cautioned that if U.S. troops were to leave entirely, he would leave a "very strong intelligence" presence in Afghanistan.