I suspect that much like Hitler he was trying to get as much territory as he could get without the international community realising what he was up to, to that end he went after Crimea and the Donbas regions, he got away with Crimea but his minions in the Donbas were as inept as his current military.
I would be more inclined to believe that his invasion of Ukraine was only because he was on the verge of failing in the Donbas as Ukraine was growing stronger but the idea that Ukraine was ever a threat to Russia is lunacy, it was only becoming a threat to Putin's plans for Ukraine.
As I recall it was John McCain and Victoria Nuland addressing Ukrainian protesters in 2013 telling them that they were there to support them...
https://www.theguardian.com/world/2013/dec/15/john-mccain-ukraine-protests-support-just-cause
Neither of those two were known for their support of the Democratic party.