Renegotiating existing trade agreements in favor of the U.S. and forcing allies to shoulder more of the cost of American troop presence have been key parts of Trump's foreign policy. He's repeatedly said the U.S. should be prepared to abandon security commitments to allies unless they make economic sense.

Last week, Trump sparked a firestorm when he said he may abandon automatic protection for NATO allies.

"I like NATO, just so you understand. I like NATO. I like the concept of NATO. It is somewhat outdated because it doesn't cover terror the way it should," Trump said Wednesday. "I think NATO's great. But it's got to be modernized. And countries that we're protecting have to pay what they're supposed to be paying." (Yonhap)