To nix the deal, the Senate must ultimately be able to vote through a resolution against it by a veto-proof majority. And that would require 67 out of the 100 US senators coming out to vote against it (along with 290 U.S. House members).
As a general principle, of course, this is probably not a strategy to be recommended. The people’s representatives should, after all, be taking meaningful votes on most international agreements.
But for a particularly delicate multilateral negotiation involving war and peace, it is an ideal setup to stack the deck against the former and in favor of the latter.
Remarkably, even the United States Constitution did not set a two-thirds threshold for Congress in making declarations of war – a feature seemingly rendered moot since World War II. A mere majority in each chamber could plunge the country into war.
It has been far too easy for the United States to choose the path of war casually. The structure of the Congressional role on the Iran Deal fortunately makes it much harder in this one instance – while still letting the “bomb bomb bomb” caucus formally register its hawkish preferences.
It might not look it to the rest of the world, but by U.S. political standards in 2015, that’s a win-win.