For the first time since 2010, the United States has released a nuclear strategy. It calls for the introduction of new and smaller nuclear weapons. Critics argue, this might set off a Cold War-era escalation, as Russia, China and North Korea are named as possible adversaries. In his State of the Union address, President Donald Trump vowed to build a nuclear arsenal "so strong and powerful that it will deter any acts of aggression
Though the United States and Russia have dismantled many weapons since the height of the Cold War stand-off, their arsenals remain formidable compared to the other seven nuclear armed nations – and they've actually got many of them on stand-by, called strategic deployment in military lingo. Those warheads are ready to be delivered by ballistic missiles or bombers. (The ones that would drop first if Donald Trump pressed his huge red button.)
For further definitions and more infos visit the expansive webpage of the Federation of American Scientists (FAS)
who is the go-to source for anything related to nuclear arsenals.