Four senators introduced legislation that would require the president to get the upper chamber's approval before changing or terminating U.S. membership in NATO.
Sens. Cory Gardner and Tim Kaine drafted the bill and Sens. Jack Reed and John McCain co-sponsored it.
The bill would require two-thirds majority support in the Senate before the U.S. can leave NATO. That's the same level of support required for the U.S. to enter a treaty.
President Donald Trump has criticized NATO and even questioned its relevance, all while trying to improve relations with Russia, one of NATO's biggest antagonists.