They did Iraq right with Afghanistan because they had the war machine out of the box and the population revved up to allow it. If they had waited, the public and Congress would have been against it. Obama tested the waters for doing a larger war with Syria in 2013 (which would have attempted to ensure the removal of al-Assad), too much time had passed since 9/11 and people were very war weary by then. With almost no support for more big wars Congress shot it down and Obama abruptly backed down.

Sept 2013: "Obama Seeks Approval by Congress for Strike in Syria"

https://www.nytimes.com/2013/09/01/world/middleeast/syria.ht...