Bluster

It’s been 6 months since that Ukraine prediction:

As both Ukraine and Russia are in their Second Turning,  it feels like this cannot get out of hand. It's going to remain internal.

This still seems correct. The U.S. doesn’t have any direct strategic interests in the area. There are advantages, perhaps, to Ukraine and Russia being separate entities, although the current state of affairs suggests that isn’t going to be a real problem. After twenty years of even nominal sovereignty, the Ukrainians won’t be hurrying to do the Russian’s bidding again. While there's still the concern that Putin might turn out to be a Very Bad Man, there's no other clear reason that might lead to involvement from others. Especially if Russia is having trouble even with what it's doing so far.

Meanwhile, there’s Putin’s reminder that Russia is not to be trifled with because it’s a nuclear power. The problem is that, while true, it is not a game changer. U.S. strategy was going to be a balancing act even if there was some sort of gentleman’s agreement limiting the weapons used.  To put it another way, the U.S. isn’t going to escalate to a Fulda Gap-level tank assault that requires a Return of Forces to Germany in order to repel Russian tanks in Ukraine. Putin’s comment is like pulling a gun out during a poker game: Whether or not it’s a bluff, it’s an acknowledgement of a weak hand. 

Finally, mentioning a strength that dates back to the Cold War risks reminding people that Soviet military technology lagged behind NATO’s. Twenty years later, there’s no indication Russian military systems have leapfrogged the competition, or have been built up beyond where they were when the Soviet Union dissolved. There were concerns even then that their ICBMS wouldn’t make it past the Arctic Circle.  Reminding an enemy of your weaknesses is rarely a smart thing to do.