I think his plan is to draw the Ukrainian forces to the East and then he will launch his ally in Belarus from the north. The hope will be to cut off the Ukrainians from their sources of supply in the West, and possibly, to encircle them.

Remember, The attack from the north need not be decisive, it only need be strong enough to force the Ukrainians to withdraw from the east to protect their rear. A small attack from Belarus need not penetrate very deeply, and may be able to elude detection by the West's satellites. Even if the Ukrainians are able to withdraw in good order back to the W bank of the Dneipr, It will leave the Eastern half of the country open to the Russian panzers.

That's what I'd do if I was Putin, but, of course, he ain't me.

But if I was Biden, I would pass the word right away that if any other country tries to take advantage of the situation the US WILL intervene and cover Ukraine's back.