The vacuum in the Middle East was the result of the destruction of Iraq as a functioning nation.  It culminated with "deBathification" which left Iraq with no functioning government and no functioning military and flooded the country with former soldiers with no source of income.

The U.S., indeed, could have "filled" that vacuum by, on a "open ended" commitment, continuing station hundreds of thousands of American soldiers as an occupying force.  Those soldiers could still be there and we could have lost thousands of American lives and suffered ten-fold that number of casualities.  The argument that "Obama caused the vacuum by pulling the troops" is totally bogus.  

The reaction to 9-11 of invading Iraq was a massive mistake, based on extremely faulty intelligence..."Iraq was responsible for 9-11 AND was preparing to launch an imminent WMD attack on the U.S."  Both assertions was simply untrue.  

Do you really feel we should have 100,000Ks of Americans fighting in the M.E.?