His idea seems to be to take the oil. Not sure we want US troops seizing oil in Iraq, Syria or anywhere else in the region. Taking it from the bad guys and handing it over to friendlies is fine. Taking it for ourselves requires quite a commitment and would make us into some modern day colonial power seizing resources. These are the kind of positions that are going to unwind Trumps run for office - unless he has a better explanation of this policy than the current one which is “We’re going to have so much money”.
I say just destroy the oil fields.
Cut off that flow of money to ISIS.
It’s going to be long time before Iraq is stable enough for anybody to want to invest there.
To put it bluntly, Trump's comment is simply loony.