This assumes that other players in Syria and Afghanistan would allow for such a development to happen. This is not at all clear; on the contrary, pulling American troops out will give others incentive to get off their asses and take care of (or adequately manage) the problem.
Conventional, status-quo foreign policy thinkers all too easily forget that other countries aren’t exactly thrilled with the notion of ISIS coming back. If anything, countries like Iran, Russia, Pakistan, Iraq, Jordan, Saudi etc are more threatened by ISIS than the U.S. is.
If America’s allies, friends, & partners are concerned ISIS will come back after Trump’s withdrawal, guess what? They can continue the mission & forge their own counterterrorism partnerships. The U.S. military’s job is to protect the American people. not to protect the region.
What think tanks like Heritage are advocating for is an indefinite U.S. military presence in both countries (how much would that cost?!) in order to kill every last ISIS terrorist. That’s neither realistic, nor accounts for the second-order consequences to our natsec strat.
Trump should focus on the NSS he published a year ago: deterring great power conflict while ensuring avenues for cooperation remain possible. Keeping U.S. soldiers in Syria and Afghanistan for another 20 years is a distraction - and yes, a huge burden on our fiscal power.
