"Red light": The military brass are resisting, even with Admiral Fallon out. The consequences would be huge, including on gas prices, military drain, and upheaval in the entire middle east if Iran was attacked by Israel with US support. Even Secretary of Defense Gates said:

"There is a lot of signalling going on. But I think everybody recognises what the consequences of any kind of a conflict would be," Gates said.

Problem: hard to contain Israel and the neoconservative administration, namely Cheney who is a rogue operative with Israel.
(Sources said that Cheney was behind the B-52 nuke displacement scandal, by-passing normal chain of command).