Entangling alliances are like abstraction. The only thing that solves it is more of it.
https://www.theguardian.com/world/2001/jun/17/russia.iantray...
https://www.wilsoncenter.org/publication/molotovs-proposal-t...
NATO is a mutual defence pact. Russia is the most militarily aggressive country in Europe. Agreeing to defend the bully when their chickens come home to roost is a tough sell.
It's not such a crazy idea really, but I'd rather we just abolished NATO entirely.
I'm no fan of Russia, but I don't want to go to war just because they shoot down a Turkish fighter plane in Syria, etc.
NATO has ensured 70 years of peace in Western Europe. There hasn’t been a period this peaceful since the Pax Romana, which still had plenty of wars. Why mess up a good thing? Less people die in wars now. And while the value in trade and infrastructure compared to land is certainly a part of ensuring the peace, that was also true for the decades preceding the Great War. The modern international order is simply more peaceful.
Once the guarantee of NATO becomes a maybe then you start having a lot of incentives for the members to make their own agreements that they can depend on. Then you would be back to regional alliances and from there rivalries. Germany's security agreement partners may not agree with Turkey's security agreement partners about what to do in Syria. Part of what made NATO work was the common interest and values of the members. As you spread it you loose that cohesion.
This is why all the baltic states have multi-country forces in them. Literally small Canadian and Italian forces are in those states, so if there is ever an invasion, those troops will the first casualties that will win the hearts and minds of the rest of NATO countries to defend because of the losses of their own countrymen.
The reason Ukraine hasn't been allowed to join NATO already is because the rest of the alliance isn't willing to make that promise (that they'll go to war with Russia to protect Ukraine).
It's doubtful Russia would go to fight Ukraine even now (it would be rather disastrous), but even more doubtful if Ukraine would join NATO.
Ukraine has its own internal problems for now.
Unfortunately it's still possible that Putin will cling to power for a rather long time.
The fact that they (professionally) can't do anything else, and that a pro-democratic alternative to Putin would likely severely cut their numbers (Russia has one of the highest if not the highest number of siloviks per capita) or even conduct lustrations against them for protecting the autocracy, plays into Putin's hand. They are also not that demanding, higher ups known to "live of the land" (protection racket etc), and Russian economy even under sanctions still a capitalist economy, so it won't be as bad as in the 80ies.
Also Russia coming under isolating western sanctions would effectively make Russia a China's tributary state, since it's the only other power with manufacturing capability Russia would be able to trade with. So that adventure would be exchanging Putin's and silovik interests for Russian future BIG time.
Also, Russia does not want to join. They want the USSR back
No, they don't, and I don't understand why people (Americans in particular?) seem to think this. Is it just nostalgia for the first Cold War?
And that weakness comes from the complete lack of the political culture needed for a functional democracy. The elite of the Russian empire that had a prototypical form of that culture had been eradicated by the communists, and about 10 years of relative lack of authoritarianism in the 90s and early 2000s wasn't nearly enough to form even a semblance of such culture. An ordinary Russian doesn't know what separation of powers is for, how freedom of speech/expression protects their interests, that it's their taxes that Putin spends, not government's money, the norms of civil debate, the individualist thinking etc etc.
In his recent easy he claimed Ukrainians and Russians are the same nation
In fact there was such a historical precedent. Turkey and Greece, both NATO members, fought a war in Northern Cyprus in 1974 [0].
[0] https://en.wikipedia.org/wiki/Turkish_invasion_of_Cyprus