What if they don't want us there? We signed an agreement to leave before, so we left. Wouldn't staying on in spite of that have amounted to a re-invasion of the country? If they had stayed then maybe ISIS wouldn't have expanded beyond Syria but the insurgency against U.S. forces would have been ongoing and many more American lives and limbs would've been lost in the mean time.
ISIS is being beaten back without massive numbers of U.S. troops on the ground so I don't think it will ever come to it. But if we had a large footprint in the country then, at any time of stability, an Iraqi leader would move to demonstrate that he's not a puppet of the U.S. and ask us to leave. And unless we want to
admitmake it look like that was what we were after all along, we'll have to oblige. Democracy is tricky business. We created a Shia bridge from Syria to Iran and the new Iraqi government is always going to answer to Tehran first. They'll use us as long as our goals match theirs and when they don't, they'll want us out. And then they'll go on persecuting the minority Sunnis who ruled them so harshly for so many years.