During the Korean War, US forces found themselves fighting not only North Korean forces but the Chinese as well. The Vietnam War had US forces fighting the North Vietnamese military armed with Soviet weapons. We did the same thing providing the mujahedeen with Stinger missiles to defeat Mi-24 Hinds in Afghanistan.
This behind the scenes support rarely works out for sponsor. China did not gain any leverage on the international scene for supporting North Korea. The Soviet Union reaped no benefits from supporting Vietnam (other than perhaps a willingness to provide weapons to oppose the US). The US support during the Soviet invasion of Afghanistan only resulted in increasing resentment of Osama bin Laden against America.
The lessons of history notwithstanding, the US has been supporting rebel forces in Syria in the hopes that it will result in the overthrow of President Asad. In two years since the beginning of the Arab spring, Asad has not only remained in power but almost thrives. The Obama Administration seems to have forgotten that the US put Shah Pahlavi of Iran into power after the invasion of the Soviet Union in 1941 forced his father’s abdication.
Shah Pahlavi’s reign was viewed as being engineered by the CIA to allow US and British oil interests unimpeded access to Persian oil fields. The resentment of the Shah and his secret police SAVAK resulted in the Tehran Embassy crisis. The Shah was sent packing and the Ayatollah Khomeini took over. The crisis led the US to support Saddam Hussein in his war against Iran. Of course, when Hussein mistook US support as a green light to invade Kuwait, the US would then form a coalition to oust its former ally from Kuwait. Relations between the US and Iran has been strained ever since.
Had the Obama Administration thought about this bit of history, they might realize that by supporting rebels in Syria only strengthens the relations between Damascus, Hezbollah and Iran. In short, Asad is not getting weaker and may actually be getting stronger. The Obama policy does nothing to dissuade Iran from pursuing its nuclear weapons program.
US forces fighting during Iraqi Freedom faced rebel forces in the north that were being supported via shipments from Syria. Perhaps President Obama thought he could turn the tables on Asad but thus far, it has thus far been for naught.