That is a very valid point, and one that has been made both by conservative commentators and army officers who were there.
Anyone who still defends the totality of our policy in Iraq (as Jeb Bush does) needs to get a handle on that point.
In reality, ISIS became a powerhouse in Syria, where they overpowered Syrian military with the help of the insurgent groups the Obama administration funded. Soon ISIS controlled 1/3 of Syria and had captured arms, tanks, jets, ordinance and supplies from Syria. Then they set their sights on Iraq. Not sure how you can blame Bush for this