Senate Majority Leader Mitch McConnell (R-KY) appeared on CNN's State of the Union Sunday and defended the letter to Iran that he signed alongside 46 other Republicans. He said its purpose is to stop President Obama from making a "very bad deal… with one of the worst regimes in the world."

McConnell said the negative reaction to their letter comes down to "selective outrage." He reminded host Dana Bash of Sen. Robert Bird flying to Moscow during the Carter administration regarding the SALT II treaty to explain to the Russians "the Senate's role in treaty ratification." Also then-Sen.  John Kerry, who during Reagan's tenure, "flew to Managua and met with the communist dictator there, Daniel Ortega, and accused the Reagan administration of engaging in terrorism."

"So look," McConnell said, "members of Congress expressing themselves about important matters, not only at home but around the world, is not unprecedented."

He continued:

So, the main point here, I think everybody needs to understand, is the president is about to make what we believe will be a very bad deal. He clearly doesn't want Congress involved in it at all, and we're worried about it. We don't think he ought to make a bad deal with one of the worst regimes in the world.