Putin is no pussycat, but he lacks the resources to really threaten the West.
That said, for the entire history of Russia, it has tried to expand its land frontiers. Sometimes it was provoked, but other times it was pure expansionism.
Perhaps NATO is outmoded. If it it, that’s a problem. By transferring the defense of western Europe to the US, it diffused regional hatreds.
For example, the Germans and Poles hate and fear each other, but not as much as they hate and fear the Russians.
What would Europe look like if Germany sees no choice, but to rearm and strengthen Poland? Everyone assumes that the German military tradition is dead. Perhaps, but if threatened, it could wake up. Germany could produce atomic weapons in weeks. It it quite capable of producing its own conventional weapons, from fighters to tanks. No need to rely on the US.
But this would certainly frighten the Russians and the cycle of tit for tat that always ends in war begins again.
Far fetched? America is turning inward and isolationist. If that continues, many countries, but especially Germany and Japan, will have no choice but to see to their own defense. Once they have the means to do so. There will be no US check on how they use them.
I find that frightening.