If they´re going to invade they´ll need to amass troops and materiel at a staging area or areas first. This takes time. Since there are no signs of such build-up now I guess we can safely assume that no invasion will take place any time soon. As for other attacks, nuclear or otherwise, well although the fruitcakes in Wash. D.C. are certifiable I doubt that even they are crazy enough for that.
An aerial attack might be suicidal for the Americans. Their fighter jets are good, but they are no match for the Russian S-400 Triumf anti-aircraft weapon system. Unless the Americans find a way for their jets to counter the S-400, I don't believe that they stand much of a chance. And a land invasion can be another wrong choice as well. In the past 600 years or so, no other nation has succeeded in invading Russia through the land-route.
In short, here are the challenges the Americans might face:
1. Russia is having more nukes compared to the US.
2. Russia is having the best and most powerful ICBM in the world (SS-18 Satan)
3. Russia is having the best anti-aircraft weapon system in the world (S-400 Triumf)
4. Russia is having the best Main battle tank (MBT) in the world (T-14 Armata).
US Air force unveils S-400 KILLER MISSILES to scare Putin
https://www.youtube.com/watch?v=A85Czh9KexI