[dragnet2]

I think a more pertinent obvious question would be why did they not stop the Russians upon entry...

And they had months notice the Russians were coming!

Same reason the Poles didn't stop the Germans at the border in 1939 - Inability to do so.

But they can easily take out Russian armor and aircraft as a matter of routine? Not buying that, no sale.

[freeandfreezing]

But they can easily take out Russian armor and aircraft as a matter of routine?

Study military tactics. One of the best ways to respond to an attack where there are limited roads, like the situation in Ukraine, is to allow the invader to come in and then attack their lines of supply.

[PAR35]

But they can easily take out Russian armor and aircraft as a matter of routine?

In a series of tactical defeats. Poles were able to take out German Armor and aircraft. The Germans lost 50 tanks and 100 vehicles in the relatively minor battle of Mokra, for example. (Although the Poles won that one).

And it took almost a week for the Germans to establish control of the air over Poland and the Polish air force put up a credible defense before running out of resources. (sound familiar yet)