According to this report, the USS Michigan is in Korean waters:
North Korea conducted a big live-fire exercise on Tuesday to mark the foundation of its military as a U.S. submarine docked in South Korea in a show of force amid growing concern over the North's nuclear and missile programs.
The port call by the USS Michigan came as a U.S. aircraft carrier strike group steamed toward Korean waters and as top envoys for North Korea policy from South Korea, Japan and the United States met in Tokyo.
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Frankly, this is a dumb PR stunt. Submarines belong underwater, not in port where they are quite vulnerable to attack.
USS Michigan apparently no longer carries ICBMs such as the Trident missile, having been converted into a cruise missile carrying sub:
That is not to say that her cruise missiles could not be armed with nuclear warheads.
It's difficult to know exactly why President Trump has called all 100 US Senators to the White House, but if I had to guess I would say he intends to attack the Koreans.
Time to stock up on duct tape, water, and cans of tuna fish.