"What would the USA do?"
History tells me we would do nothing.1983 220 Marines died. Did we go to War when our troops were killed in Beirut by the suicide bomber? Or when the Cole was bombed or even the prior incidents at the world trade center.
Hezbollah is firing new Thunder 1 rockets now which have a 12 mile range. Should be a simple matter for Israel's air to take the launching points out.
This is different. These are government sponsored attacks not from some terrorist organization. Syria and Iran are clearly involved here.