What might Putin think isn't nearly as risky as it was?
We already know he wants to get more of the states around his boarders into Russian dominance again. And he's got the armor to do it with. Should we care? Shouldn't the Europeans be doing more to defend themselves?
As to caring or not you must first ask: does our word, once given, mean anything (because that is what a treaty is)? Does the establishment of tyranny on people who have made it clear on what they think of Russian "protection" matter? We spent a lot of resource, and other needs not met, during the Reagan years saying it did. It was also an important part of who we were during world war 2. That we also didn't have the political will to tax ourselves appropriately to pay for it without a lot of added debt certainly didn't help much. Any more than following suit in Iraq or Afghanistan has done. Which then begs the question: Do the powerful want their cake, and not be bothered with the bill as they eat it too?
As to whether the Europeans should do more for their own defense is certainly a valid question. Not made any easier by the fact that may well have done so already but we're just not made very aware of it. But even then, maybe they could still do more? Still a valid question, but one that is something a reasonable people would sit down with them to talk about, and see what could be done. Not something you would just pull up stakes on and walk away from.
Consider, though, what may well already be in the works. The Russians surreptitiously move special forces into another baltic state. They put on different uniforms and suddenly declare themselves local militia rising up against Western puppet governments. It worked quite well in the Ukraine after all. But now, of course, he has more leverage to take advantage of. He has oil to sell, and an American Secretary of State who would now be anything but displeased at the thought of getting access to it. Trump is already there to decry, once again, the insufferable shiftlessness of lazy Europeans who won't defend themselves. And he will have all the cover he needs in the confusion of whether it's a genuine indigenous popular uprising or not. How easy then to just pick up stakes and walk away.
He can then, ironically or not, have the populists who voted him into office congratulate him for not getting us entangled in another foreign mess others are responsible for, even has he continues tax breaks for the rich which he will spend little of on those populist supporters. He will do that because how else might he pay for increasing those tax breaks, as he has already indicated he intends to do.
The bottom line? Our word will mean a lot less to the rest of the world. A new dictator will be given free reign in Europe, and a great deal more instability, and uncertainty will be added to the world scene. If this gives you pause there might be hope, but I'm still not very optimistic.