We could have left 50K or 100K troops in Iraq in perpetuity.
And when we took those troops out, we'd be looking at a version of what we're looking at now.
Realistically, there's only two options:
1. Do not so much, which is what Obama's doing, both politically and militarily.
2. Go into Iraq with at least 20K troops and get the government to give us the run of the country, which they don't really want to do.
As well, the only way to defeat ISIS is to deal with Syria in a serious fashion.
Which would put our ground troops in two countries, and 20K troops would escalate to 100K faster than you can say 'they'll greet us with roses'.
No real good options...I think Obama's running out the clock.