I may be a senior, but I still remember that it was George W. Bush who signed the agreement on withdrawing U.S. forces from Iraq, not President Obama.
Obama did attempt to negotiate an extension of U.S. military presence but allowed Iraq’s elected president, al-Malaki, to block it. Had Obama realized sooner that al-Malaki was sowing the seeds of ISIS by subjugating the Sunnis. he probably would have had the political leverage to take a more forceful approach to pacifying Iraq by overriding al-Malaki's objections or building a case for his removal, so he’s not blameless.
But for Jeb Bush to baldly state that Obama was responsible for U.S. withdrawal is a shameless lie.