The Constitution assigns Congress the sole authority to declare war, a decision Founding Fathers like George Mason made because they believed the executive branch was not "safely to be trusted with it." Once war has been declared, however, the president is commander in chief, which means he can use weapons — including nuclear warheads — at his discretion.
Members of the Senate Foreign Relations Committee, led by Sen. Bob Corker (R-Tenn.), have noticed that's an awful lot of destruction resting on the decision of a single person, so the committee will hold a hearing Tuesday to reconsider the president's power to launch a nuclear strike. Though the hearing has been cast in more general terms, the immediate impetus appears to be President Trump, who has threatened to "totally destroy" North Korea with "fire and fury" in a preventive strike.
Corker, who has become a vocal Trump critic within the president's party, argues the hearing is "long overdue." But the Trump administration says the current system is working just fine, maintaining that it is necessary for the president to be able to launch a nuclear strike quickly, without the delay of congressional authorization. Watch the hearing live here via PBS.