Re the question of additional parties to any potential conflict, the Bulgarian (alias Tyler Durden) who owns Zerohedge - a big Putin supporter - suggests that Biden raised the possibility of direct US involvement:
1) Wilson’s deployment of the Polar Bears in Russia proper after the Revolution
https://www.historynet.com/red-dawn-in-romanovka-russia.htm
2) the Russian air force in action over Korea
https://www.historynet.com/clash-titans-korea.htm
3) Russian air defense units deployed in North Vietnam against US aircraft
https://www.historynet.com/13703647.htm
4) the destruction of a company-sized Russian element in Syria that was raining ordnance on an American unit stationed there
https://www.nytimes.com/2018/05/24/world/middleeast/american-commandos-russian-mercenaries-syria.html
As a side note, I found this russian tv series interesting. The story of Admiral Kolchak, the last leader of the White armies in the civil war after WW1 and last head of White Russia before the reds took complete control. Lot’s of reasons why they lost. Corruption not the least of them.
https://www.imdb.com/title/tt1101026/?ref_=fn_tt_tt_2