Lots of talk about Trump's assertion, later claimed as sarcasm, that Obama and Clinton essentially founded ISIS. Overstatement? Sure. Exaggeration? Certainly. Untrue? Not even a little.
Properly stated, Obama and Clinton made decisions that we now see, with the wisdom of hindsight, made the establishment of the Islamic State or Caliphate possible, perhaps nearly inevitable. Administration bad judgments left a power vacuum in Iraq and its Shia majority began oppressing the Sunni minority as we should have predicted they would.
Shia oppression led Iraqi Sunnis to throw in with Al Qaeda in Syria and together they formed the Islamic State or ISIS. Many Sunni officers of Saddam Hussein's former army became leaders in ISIS. It became the Sunni tribes' defender against Shia oppression in Iraq and Alawite oppression in Syria.
Obama/Clinton wanted to claim an end to the Iraq war and thus removed our forces. We now see that leaving a few thousand troops would have given the U.S. leverage over what happened there and perhaps prevented ISIS.
Also their unwillingness to support President Assad, an ugly customer for sure, made the situation in Syria even more fluid and susceptible to takeover by radicals.
