"It's the job of the president to negotiate but it's the job of Congress to approve," Cotton, R-Arkansas, said in an interview with ABC News in his office this afternoon. "We're simply trying to say that Congress has a constitutional role to approve any deal, to make sure that Iran never gets a nuclear weapon. Not today, not tomorrow, not ten years from now."
"It's an unusual coalition," Obama observed.
Cotton said "there are nothing but hardliners in Iran" and explained that Republicans wrote the letter "to make sure" Iran understands that Congress has a constitutional role to approve any potential agreement.
"We're on the verge of a deal that could allow Iran to get a nuclear weapon in as little as ten years, so it's important that Iran realize that Congress will not allow that outcome to happen," he said.
Vice President Joe Biden said in a statement this evening that the letter was designed to undercut a sitting president in the wake of sensitive international negotiations.
"In thirty-six years in the United States Senate, I cannot recall another instance in which Senators wrote directly to advise another country -- much less a longtime foreign adversary -- that the President does not have the constitutional authority to reach a meaningful understanding with them," Biden said in the statement.
"The decision to undercut our President and circumvent our constitutional system offends me as a matter of principle," he said. "As a matter of policy, the letter and its authors have also offered no viable alternative to the diplomatic resolution with Iran that their letter seeks to undermine."
"Let's be very clear: Republicans are undermining our commander in chief while empowering the ayatollahs," Reid, D-Nev., said. "This letter is a hard slap in the face of not only the United States, but our allies. This is not a time to undermine our commander in chief purely out of spite."
Reid then went after Cotton, a freshman senator, who watched silently.
"Today's unprecedented letter originated by a United States senator who took his oath of office 62 days ago," Reid said. "As a kind of pettiness that diminishes us as a country in the eyes of the world. Republicans need to find a way to get over their animosity of President Obama. I can only hope that they do it sooner, rather than leader."
In his interview with ABC, Cotton dismissed Reid's assertion that the letter harms U.S. relations with several key allies.