Even before the terrorist attacks in Paris, American public opinion was moving steadily in favor of military action against ISIL, even if it meant large numbers of U.S. ground troops.
As this compendium of polling results shows, support for sending group troops to Iraq to fight ISIL in June of 2014 was low -- 30% in an ABC poll, 19% in one for CBS, compared to 77% and 65% opposed. Americans were more willing, however, to use drones [56%] and manned airstrikes [43%].
By October, support for airstrikes surged to over 70% and support for ground troops climbed to 40%.
By March, 2015, support for ground troops almost equaled those opposed, 47% to 49%. In the following months, more and more Americans voiced support for military action including U.S. ground troops: 52%-41% in August and a stunning 58%-38% in October.
I think the beheadings of hostages by ISIL has tipped American opinion into this warlike mode. The first widely reported actions were in late summer 2014, with mass killings in November, December, February,and April. Americans are disgusted by these atrocities, troubled about the chaos in the Middle East, and fearful that jihadi violence may return to our homeland. The President and Congress have a permissive consensus for military action if they wish.