The entire strategy around the United States regarding nuclear weapons, is one of deterrence.
The United States has not managed to keep up with what another superpower – Russia – has done, and while the U.S has slowly disarmed itself and let its weapons capabilities fall into a place far behind the former Soviet Union.
Russia absolutely has the firepower to completely disable the United States, they currently have submarines that are armed with nuclear warheads, they can also take out any satellite orbiting the Earth, while America has reduced the number of nuclear weapons they have and where they can launch them.
Russia has intercontinental ballistic missiles on their submarines, able to launch from port if need be. There is no need to invade anywhere, there is no need to worry that an attack might come, when your enemy is not able to compete.
The West could potentially be defeated with only one nuclear warhead and Russia has already threatened to detonate a nuke under the sea near the United Kingdom, which would cause a mega tsunami.
A nuclear weapon detonated over the U.S could fry every single electronic device and the electric grid itself, which is a state of disrepair already.
Fact is, a war with Russia will have bad outcomes and from the looks of it, America may not be the one that comes out victorious if the world stays on the current trajectory.