Admiral James Stavridis, who speculated that one possibility could be Putin's perceived need to have a "land bridge" to Crimea by not taking over all of Ukraine, but rather just the eastern segment of the country that is fairly heavily populated with Russian sympathizers...any other part of Ukraine would be a blood bath for him (not to say he wouldn't try)...stay tuned for more reports on the scheduled call between Biden and Putin next Tuesday.
Another theory discussed was the possibility of Putin "Saber Rattling" to dissuade Ukraine from going 'All In' on NATO membership...again, a likely topic on Tuesday's Zoom call.