This former US Navy pilot I know, my father, insists that invading Iran would be a logistical nightmare due to the surrounding geography.  
Where would we get the troops? We're already stretched way too thin and have "eaten the seed corn" in some cases to get expert personnel to Iraq.

We'd have to strip our forces in Afghanistan and Iraq . . . and there still would be insufficient troops. Not a workable plan.

What we do have an abundance of is strategic air power. After their electricity is gone, so is any potential to make nuclear weapons.

Gimme a D
Gimme an R
gimme an A  = F =  T

what's that spell?     oh sh*t

looks like we'll be headin' to Canada for more than strong beer and cheap drugs.

 To be honest/serious, though::
I can't imagine the US public getting behind another war, let alone one requiring a DRAFT.
This isn't 1941. Maybe I'm underestimating the Rummy/Fox News Right. Could they be so patriotic?
Heaven help us.