False premise right off the bat. How exactly does Ukraine joining NATO threaten the existence of Russia? The only thing it threatens is Russia's desire to rebuild its historical empire by dominating Ukraine and who knows what other ambition.
Here’s how I know NATO is no offensive threat to Russia.
NATO could totally kick Russia’s butt right now and doesn’t do it.
Russia can’t even beat Ukraine after 3 years and it’s bogged down there.
NATO could easily defeat Russia IF it wanted to and doesn’t need a battered Ukraine to do it.
Or NATO could just go into Ukraine and do it there.
Instead NATO is busy building defenses against a RUSSIAN attack on the Baltic states.
Of course this is a conventional war discussion. NATO also won’t attack Russia because of the nuclear deterrent.
The only one who got Russia invaded in this war is Russia - twice.
Bingo. That has always been the "NATO" issue. Not a Russian fear of being attacked, but a "fear" that it would not longer be able to attack its neighbor.
“How exactly does Ukraine joining NATO threaten the existence of Russia?”
Because it borders Russia. And Putin and the Russians are the ones to consider when they think they are being threatened.