Taken out of context. He's meaning to say that because of the wars in Iraq and Syria (which Bush is to blame for too seeing as it dates back to the 90s) has resulted in ISIS in the middle east and thus the aforementioned people have "created ISIS".
We know that ISIS (what I shall call them for the basis of mutual understanding) began with Zarqawi in the early 90s, he met with Laden and chose not to join al-Qaeda. After Taliban in 2001, he then flew to Iraq. Because of the Bush admin, tensions built among terrorists groups (and Muslims alike) cumulating in the formation of IS whilst the main target was Iraq / Hussein.
Shortly after 2003, ISIS (then known as Jama’at al-Tawhid w’al-Jihad) was already a group to be reckoned with.
Several years later, Obama became the President of the United States. He formed ISIS? I don't think that's possible.
The origins come from a little earlier - in 2004 or earlier.
Isis: the inside story
One of the Islamic State’s senior commanders reveals exclusive details of the terror group’s origins inside an Iraqi prison – right under the noses of their American jailers.
Most of his supporters will just believe it and blame Hillary without questioning and if they check the facts, it probably reflects badly on Jeb Bush, in which case it's still a win for Trump.
It might not go down so well if he attacks Bush directly.
This way is smarter.
