LUHE: Since you haven't read about Putin your claim that Russia today vs. Cold war is different in relevant ways insofar policy is concerned is a bit hollow. If you have relevant literature on the subject I would like to see it, but quite frankly I find this "you read A, now I say B, try to disprove me" is a bit tedious.
Would they have stopped Putin from annexing Crimea, had they been in place?
If you have an iPhone, you can ask Siri.
This is a complex question but irrelevant: What matters is which policy will discourage the current behavior from the Putin regime. One where his behavior has clear, tangible consequences or one where he gets a slap on the hand and sanctions are then lifted.
You argued that what the US should do with Russia is lift sanctions and pursue common goals in Syria. This is something I have only seen warnings about and which I don't understand what means since Russias goal in Syria is an alliance with the Assad regime and further destabilization of EU. Terror in the EU by Muslims is a feature not a bug from Putins perspective, if not, you have to explain to me why a stream of refugees in EU in any way should be bad from a Russian perspective.
I think you mean when the USSR was a superpower? I think we should be careful not to conflate the Russia of today and the USSR of the 80s.
In which way are Russia and USSR relevantly different?