If Putin chose to take Poland, those 5,000 men and women from Ft Carson would just be a minor speed bump in the process.  Three-seven days max; by then they would all be dead or captured.  "Quantity has a quality all its own." is taught in places like West Point.  

Unless we choose to go nuclear, we couldn't respond for months.  Look how long it took us to get the initial troops to Saudi Arabia back in Gulf War I.

I see him keeping enough troops milling about on the other side of the Polish border to keep our attention  while his current Spetsnaz troops and the ethnic Russians moved to the Eastern Ukraine by Stalin after he killed off the 7 million kulaks there continuing their efforts in Ukraine and daring us to do anything about it.  

We have no responses to deal with that.  

The Budapest Memorandum between the US, Russia, Ukraine and Great Britain has already been violated by Putin and his Spetsnaz attacks.  

We have done nothing about it except some wimpy Obama 'sanctions'.