Thank you for that post Rickair. Rather than imply that Vindman was some sort of political thug, perhaps his patriotism and sense of duty should be respected.

While I have no proof, I strongly suspect that the famous phone call was only the last straw for Vindman. It was well known that Ukraine was on the administrations S... List ( GOP support for Ukraine was officially dropped from the GOP platform after D. Trumps nomination in 2016. It was the same in 2020 as the platform was essentially a copy and paste from 2016). Fundamentally the Chief Executive favored, and was obsequious to, V. Putin and (his)Russian interests while obstreperous and disruptive to European Allies and our NATO commitments.

Regarding Ukraine (and anything else high on Putin's interest list) my information has it that it was a continuous struggle in State to prevent ongoing sabotage of Donbass region intel, aid, positive reporting, and general cordial relations. I gathered it was to the point that careers were both risked and damaged.
My take is that Vindman decided someone had to "Bell the Cat". While no one dared openly say what was widely believed regarding the former President's relationship with an unfriendly foreign power, they COULD state publicly what was verified factual behavior.