Musk, who is advising U.S. President Donald Trump on plans to shrink the U.S. government, was responding to a post on X calling for the United States' exit from NATO. "We really should," wrote Musk. The 32-member North Atlantic Treaty Organization includes much of Europe, the U.S. and Canada.

Trump said he told NATO allies that if they’re not going to pay their bills, he won’t defend them.

Trump has repeatedly criticized Europe's defense spending and previously threatened to leave NATO if allies didn't pay more.