The argument about NATO really goes back to the 1999 when George Kennan called the expansion of NATO into Central Europe “the most fateful error of American policy in the entire post-Cold War era.” At that time, Russia had suffered through an entire decade of negative GDP growth and was a threat to no one. Kennan saw an opportunity to integrate Russia into the west following the collapse of the Soviet Union and believed that NATO expansion would force Russia into an adversarial relationship with the West. As NATO continued to expand towards Russia's borders with a huge expansion under W Bush in 2004, the issue of NATO expansion took on global significance as the US began positioning missile defense systems in Europe based on the pretext that Iran or N. Korea may have ICBM nuclear capabilities. But missile defense systems in Europe are first strike weapons against Russia in that they can stop a Russian counter attack if the US strikes first. This potentially means that the US can threaten a nuclear strike if Russia does not follow what Washington wants. Russia made it clear in Syria and Crimea (and now Ukraine) that it would not play that game. So it is really not that clear whether Russia really gives a crap about NATO expansion. Russia has no problem using nukes if a single NATO soldier sets foot on Russian soil. So, NATO expansion is of limited relevance in that the Clinton and W Bush administrations had a chance to craft a much better relationship with Russia and chose instead to expand NATO to line the pockets of defense contractors. But today, I think Russia is well beyond considering NATO a threat and carries out whatever military actions it wants regardless of NATO.
I think Russia's current moves have a lot more to do with Putin's domestic politics and his fears of economic stagnation and corruption in Russia causing a rebellion like what happened in Belarus and Kazakhstan. When Russia took Crimea, Putin's popularity shot through the roof even though the Russian economy subsequently crashed due to the oil glut of 2015. NATO is just a pretext at this point. Germany and France were willing to offer NATO concessions in talks before the invasion, but Russia had demands for NATO that were obviously non-starters or poison pills (Russia wanted to be able to tell NATO where it could position forces). So, I think this invasion was going to happen regardless of Ukraine seeking NATO membership (which really wasn't on the agenda).
So, the West could have prevented this but that may just be 20/20 hindsight because the time to build a different relationship with Russia was over two decades ago. Thus, it is more fodder for academics than anything that is relevant to the current war in Ukraine. I think Russia did this on its own because Putin thought that Ukraine would cave quickly like in Crimea and help boost Putin at home.
The progressive left has generally been anti-war, which is appropriate. But I think there has been a failure to see that Putin really is just a bad actor and is a danger to the West because the progressive left is still mad about all the effort the neo-liberal/centrist DNC dems spent chasing Russiagate. Bernie has taken the best position on the war and wants to provide Ukraine with as much support as possible without risking an escalation of the conflict beyond Ukraine's borders. But others in the progressive wing seem to think that starving Ukraine of military support would lead to peace and save lives because Russia will inevitably win the war (and military support for Ukraine may have a blow back issue with empowering the neo-nazi elements of the Ukraine armed forces). But the major premise of that argument is the belief that Russia is a rational actor and has been provoked by NATO expansion. I just don't think that is the case and the progressive left needs to wake up to the possibility that Putin is just a bad actor without rational political motivations.
Conversely, the neo-liberal centrist Dems, particularly think tank denizens and anti-Trumper converted neo-cons, are pretty reckless in their efforts to try to counter Putin's aggression. No fly zones, fighter jets, etc. are all clearly actions that will result in Putin attacking NATO targets and quickly escalating the conflict into a potentially terminal nuclear war. To his credit, Biden has been very solid in guarding against escalation as have other NATO leaders.