"We can suppose that Syria learned from Iraqi and Libyan experience and obtained a sufficient amount of GPS jamming devices from Russia. Hundreds or thousands of these devices can easily cover a large area around Damascus and other important areas, so that cruise missiles would fly off course by hundreds of kilometers. The GPS jamming zone can start over water, where TERCOM and DSMAC guidance surely do not work. With the use of small boats, a jamming zone can be extended hundreds kilometers from the shore.
An additional restriction is that the presence of advanced anti-ship missiles supplied by Russia does not allow American ships to come close to Syrian shores for the attack, so missiles have to fly long distances over water, likely without a GPS signal, and this will lead to difficulties in resuming TERCOM navigation when overland." Asia Times
This author claims that the US was simply unable to achieve a desired level of destruction in Syria because of technical reasons and for that reason Obama yielded to public pressure and went to Congress for approval of air action where he knew he would loose.
I don't believe that is what happened but I leave it to the air techno boffins to deal with this argument. pl