He’s taking advantage of a weak Biden.
But, he miscalculated badly on Ukraine resolve.
Russian military credibility ruined forever...the real Paper Tiger.
They have no supply lines in the cities. If they go in it is going to be a horrible fiery death for many Russian APC and tanker crew. Running out of gas deep inside a city will not end well.
In short, a repeat of the Battle of Berlin 1945. The Red Army suffered a huge amount of vehicle losses because German defenders with antitank weapons like the Panzerfaust picked the vehicles from hidden positions. Russian armored vehicles will be subject to attack from a long list of anti-armor weapons the Ukrainians possess, even the old SPG-9 73 mm recoilless antitank rifle.