By Jim Sciutto
The Obama administration's efforts to negotiate a final deal with Iran over its nuclear program faces a potential new hurdle as the Senate moves toward a veto-proof majority supporting legislation authorizing new economic sanctions on Iran.
The bipartisan proposal introduced by Foreign Relations Committee Chairman Sen. Robert Menendez, D-New Jersey, and Sen. Mark Kirk, R-Illinois, now has 59 senators who have formally committed to support it, a senior Senate aide tells CNN.