Misguided policy makers in the United States have previously tried to get approval to attack Iran in January 05 and 06. In both these cases the Iran hawks were turned away from their disasterous undertaking by a chorus of dissent from all our allies, most of the people in Congress and most of our seated and retired generals.
This time, the attack Iran lobby knows that going in. Therefore, they may have arranged for Israel to bomb Iran and for the US to join the party after Israel gets it started. This would bypass any Congressional approval because the war would already be on once Israel dropped our bunker buster bombs on Iran, Iran retaliated in any way, and the US responded from it's aircraft carriers and subs in the Gulf. It would be too late for Congress to disapprove.
Since this nefarious plan requires that Israel light the fuse, then the planners in Israel's War Cabinet must be stopped. The best way for the Netroots to do this is for each member to contact his Congressional representatives urging them to inform Israel that if it attacks Iran Congress will withdraw it's generous funding of billions per year to Israel. The most effective way to stop this potential Armageddon is to tell Israel not to pull the trigger.