What they're trying to do to Syria is precisely what they did to Libya.
Move in Sunni Jihadists from surrounding war-torn and chaotic regions like Iraq and Afghanistan with Saudi-Arabian money and support, tether these Jihadists to Sunni groups/movements within said country, claim the country is engaged in a 'civil uprising' and that the Government's efforts to suppress these Jihadists are heinous attacks on citizens, and start invading/bombing the fuck out of the country's infrastructure in order to 'help'.
One of the most shameful moments of modern western civilization to my mind was the big old party we threw when Gaddafi was lynched; how we celebrated a man being beaten to death brutally in the street with no accountability... here in Canada, we actually threw a Canadian working as a bodyguard for Gaddafi out of the country on the suggestion he was culpable for Gaddafi's crimes because he DARED to rescue the man's wife and child from precisely the same gruesome fate.
What's been going on in Syria is more or less the same situation. The country finds itself inundated with Sunni Jihadists, indeed with a fair deal of support from the existing Sunni population, and when Assad starts combating the forces we'd under any other circumstance describe as Terrorists, we claim a terrible civil war is underway, Assad brutally murdering his own people who simply want freedom from his evil regime (and Sunni-Islamic Sharia-style Religious Rule of a currently secular and inclusive nation). America, righteous representative of goodness and freedom, comes to the aid of these noble rebel forces, but acknowledges that there are also evil Sunni-Jihadist Terrorists called ISIS (who have nothing to do with the freedom-loving Sunni-Jihadist rebels, we swear!) and so starts dropping bombs on Syrian Oil-Refineries, Syrian gas plants, all makes of Syrian oil-infrastructure for the noble purpose of 'cutting off ISIS funding', all without Syria's permission, which would be extremely illegal if America cared about international law in the slightest when they're not enforcing it themselves.
What Syria has that Libya didn't however is Russia's full support. Russia eventually called America's bluff in Syria, got the Syrian government's permission to intervene, and with their support and coordination Syria was able to rapidly turn the conflict around, going from ISIS near conquering Aleppo to ISIS generally on the run in only a few short months. While America had been 'helping' defeat ISIS for years to no apparent effect, Russia has generally defeated the Sunni Jihadists at every turn, all in accordance with international law, something which should be quite embarrassing if America actually had any shame regarding its true intentions.
As Assad's position is now solidifying rather than deteriorating, and America is put in the position of having to declare War on Russia if they want to get rid of him in the same way as they did Gaddafi with a 'No Fly Zone' (modern double-speak for a massive bombing campaign), America is looking for ways to either get around or more alarmingly justify such a terrifying move. So here we are, with yet another "Evil Assad and his chemical weapons!" story. CIA talking heads are showing up on the news and TV talk shows such as a recent release of Bill Maher's show, and actually making the nutso-bonkers claim that Assad and ISIS are in cahoots, in spite of it being a widely downplayed fact that the biggest sponsor of ISIS is the Saudi-Arabian government, an enemy of Syria and America's biggest ally in the region.
I don't 'support' Assad, I didn't 'support' Gaddafi, but to destroy and dismantle entire nations, leaving them chaos-filled cess-pools of religious extremism and barbarism, just to oust an unpleasant figurehead makes no moral sense. Name me a leader of a nation with an actively engaged military who isn't a killer and crook responsible for War-Crimes in someones eyes. Libya wasn't some horrible place prior to America's intervention. It was by most measures the wealthiest, safest, most stable nation on the African continent, and rest assured, it's none of those things anymore. Syria too, while no paradise, is a secular democracy where one at least USED to be able to be a Christian, a Buddhist, a Jew, whatever, with the full expectation no one's going to cut off your head. If Assad loses, that's all over.