Of course that's what they have to say.
But that's bullshit bluster and the call would/will need to be made at the time according to Russia's use of a tactical nuke.
No country is going to jump right into a nuclear war because of the use of a tactical nuke.
In a way, I think you are right. But the result would be the same as if they had just jumped in.
The US, having drawn a line, would have to respond. Probably their response would be to declare a no fly zone over Ukraine or start actively helping Ukraine. I mean actively, instead of just sending bombs and bullets.
Russia would see this as an escalation, and probably launch another “tactical” nuke. The US would respond by bombing the weapons depots inside Russia, either with Stealth aircraft, or with Cruise missiles. and every action would be an escalation from the previous one.
Eventually, and it would probably take days, or perhaps a few weeks, the full Nuclear War would start. Each side would see each step as vital to their own survival and place. Bombing would come when either side felt they were back into a corner, and left with no alternative.
Putin is likely to do it. Yes, he’s got to be smart enough to understand his position. But his Position is a bad one. Russia doesn’t have a long history of peaceful transitions of power. And people like Putin, strong men, arrogant men, don’t lose with grace. They are the epitome of the term Bad Loser. Putin almost certainly faces assassination should he lose his position as President. And after all that has been expended in Ukraine, he can’t pull back without Victory. If he does, his position is history.
His family, and Mistress are all safe in secure bunkers. And it is Victory of Death for him. But we can’t let him win. If we do, we start the wars of Imperialism all over again. We can’t do that either. It will certainly lead to all out Nuclear War.
Each day is another step in a Minefield.