No argument about it, it isn't a new conflict and the AUMF is still valid.Yes, but Trump himself Tweeted multiple times that the President should seek approval from Congress before starting another conflict. Not to mention the 6 years of tweeting that we should get out of A-Stan.
From 2013:
https://twitter.com/realDonaldTrump/status/373581528405905408
https://twitter.com/realDonaldTrump/status/373146637184401408
You could argue we're not actually in a new conflict, just a continuation of a very long one. You could even argue the AUMF is still current, and he can do what he damn well pleases. You'd be correct on both points.
I'd like to see a goal in all this. All I've seen is perpetual war with each President using a different reasoning behind sending in more troops.
As to the President's previous position he covered that during his speech last evening, to paraphrase he said - Arm-chair quarterbacking ain't nothing like being in the game. His position has changed, though I am sure he would like to find a way to get us the Hell out of there, but now realizes it ain't that simple.
The goal, from what I got from his speech, is to prevent the mess in Afghanistan from looking like the mess after the 2011 withdrawal from Iraq, to maintain a presence until such time as the Afghans can govern themselves effectively, in the process we are going to be killing terrorists. Giving our "war fighters" the ability (and localized authority) to conduct war as necessary to eradicate those that want to make war even if it means going in to Pakistan.