Sign and ratify the Treaty on the Prohibition of Nuclear Weapons (TPNW).
Most people believe nuclear weapons are an important asset to national security and peace, but nothing could be further from the truth. They are a HUGE liability that could, at any given moment, trigger nuclear winter, kill billions of people, and end civilization as we know it.
The important diplomatic element of signaling U.S. resolve to act on nuclear disarmament is the main reason to urgently sign and ratify the TPNW. Other countries, especially those with nuclear weapons, will understand that we are serious about achieving a stable and prosperous global peace when they see us ratify the Treaty.
This should be a top diplomatic and legislative priority of the new Administration.