We cannot leave without a stable Iraqi government and effective security forces in place. Cannot. Period. If we do, Iran or Syria will rush in to fill the power vaccum left by our withdrawal. And Iraq isn't ready to stand on its own. And I hate so say that, because I don't relish the thought of rotating back here any time soon, but that's just the way it is.
When we started building up this government and these security forces, it was like giving birth to a baby. Well, that baby is now a fussy toddler. Do the mental extrapolation for yourself to see how long it should take for that toddler to grow up and be an independent adult. (All strictly IMO and not official, of course)