https://www.americanthinker.com/articles/2018/12/president_trump_is_right_about_syria.html
On the campaign trail in 2012, President Obama took credit for ending the war in Iraq and bringing all U.S. troops home from that country. Military leaders quietly decried the evacuation of troops from Iraq. To do so created a vacuum for hostiles, such as the displaced Baath Party members loyal to Saddam Hussein. In early 2014, the Islamic State in Iraq and Syria appeared, rolling through the upper third of a largely unarmed and unprotected Iraq, setting the country ablaze.
Although removing U.S. forces from an unarmed Iraq was an obvious blunder, by September 2014, President Obama was dismissing complaints of his handling of the outbreak of hostilities. He declared that ISIS was the equivalent of “a jayvee team” and was nothing to worry about. In 2016, we learned from Secretary John Kerry that regime change in Syria, the removal of Bashar Assad, was the Obama administration’s goal. Focused on this agenda, the White House intentionally gave arms to ISIS, betting that ISIS’s success would force the Syrian president to acquiesce toward Obama’s terms and step down.
U.S. political and military leaders knew that Iraq was working to build up its military, but it had not been able to reconstitute its armed forces in effective numbers. They knew that Iraqi recruits and pilots were in schools run by Americans and taught by Americans. The timing was right for war, as Iraq was utterly defenseless if ISIS came to town.