What the fuck do they think is going to happen if they keep putting pressure on Syria? That there'll be a peaceful revolution that will put pro-US government in Damascus?
Have they sat down and thought about it at all? Have they, for example, considered whether there are rival sects or ethnic groups in Syria?
Here's a clue from the CIA world factbook :
Religions : Sunni Muslim 74%, Alawite, Druze, and other Muslim sects 16%, Christian (various sects) 10%, Jewish (tiny communities in Damascus, Al Qamishli, and Aleppo)
Languages: Definition Field Listing Arabic (official); Kurdish, Armenian, Aramaic, Circassian widely understood; French, English somewhat understood
OK, maybe it's time for a fun, wacky conspiracy theory. The US knows it's in for a dangerous time withdrawing from Iraq. So what it wants to do is make a dash west to the safety of Israel. But if it can spin that as an invasion of Damascus (to protect poor little Lebanon) ... :-)