With our troop level the lowest since WW2 can we defend our nation?

Yes, However the likelihood that we will need to use "Tactical" Nuclear Weapons in the defense of the nation has never been greater.

Besides the military there are millions of civilian firearm owners, like myself. Should we come under attack, I would first try and re-enlist into my MOS - 68W Combat Medic, despite being partially disabled. I'm sure every gun owner feels the same; in that they will also defend this country right along side the military.

Our current model of "Defense" is through Global Stability. If you put "Brush Fires" out, you don't worry about "Forest Fires." The idea is that a much smaller military is needed which acts a global arm going where it is needed in a timely manner, rather than a larger one for "one off" purposes.