Sen. Tom Cotton has "no regrets" about sending a letter to Iran threatening to undo any deal reached with the U.S., the Arkansas Republican said Sunday on CBS’s Face of the Nation. “Iran’s leaders need to hear the message loud and clear,” he said, defending the letter signed by 46 other Republican senators. Cotton emphasized that any deal struck with Iran needed to be approved by Congress and could be amended after Obama leaves office. Secretary of State John Kerry earlier slammed the GOP letter “unprecedented” and incorrect. Congress does not have the ability to change executive agreements, he said.