Sen. Tom Cotton of Arkansas said on Tuesday that he was not trying to undermine President Barack Obama when he wrote a letter, signed by 46 Republican colleagues, warning Iran against making a deal with the United States on its nuclear program.
"This is about stopping Iran from getting a nuclear weapon," he said on MSNBC's "Morning Joe."
Obama said on Monday that the Republicans who signed the letter "want to make common cause with the hard-liners in Iran," and Vice President Joe Biden said that they were trying an end run around the constitutional separation of powers.
Iran says that its nuclear ambitions are peaceful, and the Obama administration, which is working with five world powers toward an agreement, says that a deal is the best way to keep Iran from developing a nuclear weapon.
The letter from the Republican senators warned Iran that a deal without congressional approval could be reversed by the next president. The New York Daily News branded Cotton, and the other Republicans who signed it, traitors.
On MSNBC, Cotton said that the only acceptable deal with Iran would require "complete nuclear disarmament."
"They are nothing but hardliners in Tehran," he said. "They've been killing Americans for 35 years."
He also took a shot at the vice president: "Joe Biden, as Barack Obama's own secretary of defense has said, has been wrong about nearly every major foreign policy and national security decision in the last 40 years."
The reference was to a memoir by former Defense Secretary Robert Gates.