WASHINGTON (CNN) -- A heated exchanged between President Barack Obama and Sen. Robert Menendez (D-New Jersey) broke out Thursday over whether the U.S. should reimpose sanctions on Iran amid ongoing negotiations over the country's nuclear program, according to two senators who were in the room. Menendez, the leading Democrat pushing for additional sanctions against Iran, forcefully pressed Obama on the need for additional sanctions during a meeting in which Obama urged Menendez and other senators to drop their efforts to pass sanctions legislation. Additional sanctions, Obama argued, could torpedo ongoing negotiations over Iran's nuclear program. The unusually sharp exchange, between...