I’m against it too but this was not exactly a flip flop or change for Trump. Sure back four or five years ago he critizized Obama and wanted out of Afghanistan but last year as a Presidential canidate he was for staying:
DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: I would stay in Afghanistan. It’s probably the one place we should have gone in the Middle East because it’s adjacent and right next to Pakistan which has nuclear weapons. So I think you have to stay and do the best you can, not that it’s ever going to be great but I don’t think we have much of a choice. That’s one place, frankly, instead of going to Iraq we probably should have gone there first. I would say in Afghanistan and only, again, because of its location next to Pakistan.
O’REILLY: All right. So you would keep the 10,000 troops there. And fight a war of attrition against the Taliban? You know, Pakistan —
TRUMP: I hate doing it, I hate doing it so much. But, again, you have nuclear weapons in Pakistan so I would do it.
http://www.foxnews.com/transcript/2016/04/29/donald-trump-on-his-foreign-policy-strategy.html
That was the Obama team’s view: Afghanistan was supposed to be the “good” war and Iraq the “bad” one.
And the alternative being advocated wasn’t to leave, but not to ramp up our troop and treasure investment there.