One very important thing to watch - large-scale mobilization of Reserves and National Guard units. Should this happen, shit's going to get real. As I remember, each Active Army (Regular Army) division has a National Guard "round-out" brigade. In addition, Civil Affairs is handled only by the Army Reserve.
After Vietnam, we moved to a volunteer military. Last draftees left in 1975. Actually saw a few Army draftees when I was in language school 74-75. The Army consciously went to a "total force" concept, deliberately dividing up various missions between the regulars and the reserves, to stop people saying the reserves and NG get to stay home while the regulars went out to fight. Everyone has skin in the game from day one.
Air National Guard can mobilize fairly quickly. They could go overseas, or stay here and backfill while regular units went overseas. AF Reserve could also get into action fairly quickly. Will take National Guard longer to get "round-out" brigades combat-ready. This was a problem in Desert Storm. Believe at least one NG brigade never became combat-ready enough to go to the Middle East. Cannot speak about Navy and Marine Reserves, no National Guard for them.
To those living in NATO countries, keep an eye out for similar mobilizations.
Another sign of anus-clenching adventure to come would be if people started getting drafted. Machinery has always been in place, men must register at 18. However, likely would take 6-9 months to produce combat-ready infantry replacements from the day the first men were called up.