>>the Pentagon was thinking about going back to Afghanistan

Of course they were. Their job is to have a plan for every possibility, no matter how remote. Remember that the Pentagon (or the JCS) doesn't make the decision to go, but if there's a political leader who thinks it's important, they better be able to say "here's how it might work, here's the resources needed in each case, and here's both best-case and worst-case on how it'll go".

I can't see the US back there unless AlQaida or Isis sets up there, starts launching attacks on the US - and the gov't of Afghanistan refuses to do anything about it (or is complicit).