President-elect Donald Trump made waves on Thursday by tweeting that the US must “expand its nuclear capability” until “the world comes to its senses.”

It’s the latest in a string of remarks the president-elect has made, either during the campaign or following its conclusion, that have raised some eyebrows about the US’s nuclear arsenal.

His prior statements led some to question: Could a president make the decision to use a nuclear weapon without any interference from others?

Bruce Blair, a former Minuteman missile-launch officer and research scholar at Princeton University’s Program on Science and Global Security, told Business Insider in September that the answer, essentially, is yes.

Blair pointed to a step-by-step outline of the nuclear chain of command, which he helped describe in Bloomberg earlier in September.