"At this time it would run counter to U.S. interests to seek to openly undermine Hezbollah in Lebanon"

"...Given all of the provocations and reprisals, it is in many respects surprising that Lebanon's sectarian infighting has not already boiled over into a civil war. It appears that radical Sunni groups and the FSA are specifically targeting Hezbollah interests and the Lebanese army in order to provoke counterattacks that would discredit the military and spark broader resentment of Hezbollah within the Sunni community. This strategy makes it increasingly difficult for the Lebanese army to intervene when it might be seen as benefiting Hezbollah without risking damage to its veneer of neutrality. It could also make it harder for Hezbollah to maintain political coalition partners. Aware of the costs, Hezbollah has avoided rising to the bait, but if it continues to stand by as its soldiers and supporters are assassinated it could quickly take a toll on the resistance group's morale and internal cohesion at a time when Hezbollah leaders are already asking members to make huge sacrifices by fighting in Syria.
While the United State has taken a clear stance in support of the FSA in Syria, in Lebanon the Obama administration has strongly advocated neutrality. Yet, if Hezbollah's participation in the Syrian civil war begins to clearly tip the balance in favor of the Assad regime, the administration could face pressure to adjust its position and support efforts to minimize Hezbollah's position in Lebanon. But the benefits of increasing anti-Hezbollah sentiment in Lebanon, or in diverting Hezbollah resources and attention away from Syria, would likely be quickly outweighed by the spread of radical jihadism and a descent into civil war. Radical Sunni elements would be strengthened in part because the prospect of fighting Hezbollah -- a Shiite organization aligned with the Islamic Republic of Iran and advocating the establishment of Shiite clerical rule -- is even more attractive to jihadists than fighting the quasi-Shiite, ostensibly secular, Assad regime. Open conflict would likely ensue because an embattled Hezbollah would be forced to use its primary advantage over all other Lebanese groups -- its sizable arsenal -- and doing so would force other Lebanese groups to mobilize for a showdown.
The Obama administration is already torn over how to supply arms to the FSA. If a broader civil conflict broke out in Lebanon, it is doubtful that the United States could commit the type of support required to tip the scales in favor of anti-Hezbollah groups, especially if Salafi jihadists are manning the frontlines. It is also unlikely that either Israel or Iran could sit on the sidelines if such a conflict occurred, and their involvement would both raise the stakes and further complicate matters for the United States. Hence, even though the United States has designated Hezbollah a terrorist organization, and finds itself supporting those battling Hezbollah in Syria, at this time it would run counter to U.S. interests to seek to openly undermine Hezbollah in Lebanon. "