Earlier quoted context omitted.
>In fact, the US has had to tread very carefully simply to place missiles that are capable of carrying nuclear warheads in Poland, which is a neighbor of Ukraine. according to Putin that treading is a major motivation for his current actions.
That's correct. You don't put missiles in range of a nuclear superpower's population centers and expect them to ignore it. But I feel that the timing of this is more related to Putin's political situation at home.
yes, as i already wrote during the last year, Ukraine got Turkish drones and with them the window of opportunity to win the Donbass war (like Azerbaijan/Turkey did against Armenia/Russia). The fall of Donbass would have been a large failure for Putin which his regime would have hard time to survive. Without bringing aviation though Russian forces couldn't operate successfully there (especially given the tank swallowing deep Spring mud what is going to happen in few weeks), and this is what happened yesterday across Ukraine - attacks on airfields and air-defenses, command and control centers, etc.