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Sen. Tom Cotton has "no regrets at all" over GOP letter to Iran

Last Updated Mar 15, 2015 12:53 PM EDT

Sen. Tom Cotton is standing firmly behind the controversial letter he sent to Iranian leaders regarding ongoing nuclear negotiations with the United States.

"It's so important we communicated this message straight to Iran," Cotton said Sunday on CBS News' "Face the Nation," adding that he had "no regrets at all" for his communications with Tehran.

The Arkansas senator, who now serves on the Foreign Relations Committee, stood behind the warnings in the letter, signed by 46 other Republican legislators.

"It's a simple fact of our constitution that if Congress does not approve that deal, then it may not last," Cotton stated, further asking for the executive branch to "call [Iran's] bluff" in the negotiations.

"The Iranians frequently bluff to walk away from the table," the legislator said. "If they bluff this week, call their bluff. The Congress stands ready to impose much more severe sanctions."

"The congress is ready to impose much more severe sanctions," the Arkansas senator said, echoing Israel Prime Minister Benjamin Netanyahu's words that "the alternative to a bad deal is a better deal."

Secretary of State John Kerry also appeared Sunday on "Face the Nation," blasting Cotton's letter as "unconstitutional" and "un-thought-out."

"I'm not going to apologize for the unconstitutional, un-thought-out action by somebody who's who's been in the United States Senate for 60-something days," Kerry told CBS News correspondent Margaret Brennan. "That's just inappropriate."

The newly-elected senator responded with his "surprise" to Kerry's comments.

"Just a few days ago, he testified before the Senate to say that any deal would not be legally binding. Now he says that future Congresses can't change a near executive agreement if we disagree with them, or if a future president disagrees with them?" Cotton said. "That's not the way our constitutional system works. And it's certainly not the way we should be negotiating with Iran."

"It's certainly not the way we should be negotiating with Iran," the junior senator asserted.

He also criticized the Iranian response to the letter, saying that their Foreign Minister, Mohammed Zarif--who last week called the GOP message a "propaganda ploy"-- does not understand the workings of American governance.

"He thinks international law can override our constitution," Cotton criticized. When referring to international treaties, the Arkansas legislator said that "Congress has to approve them for them to be lasting and binding."

Cotton asserted that his staff "did reach out to some Democratic offices." However, Sen. Joe Manchin, who also joined "Face the Nation" Sunday, maintained that "no one from my staff said anyone had approached them."

"I think it was wrong," Manchin, who also serves on the Senate Foreign Relations committee, said. "I would not have signed it, but I was not approached."