Republican Sen. Roy Blunt Stands by Iran Letter “No deal is better than a bad deal," he says.

 -- Sen. Roy Blunt of Missouri does not regret signing the open letter to Iran’s leaders warning of the limits of a nuclear deal with the Obama administration, unlike some of his Republican Senate colleagues.

“I really don’t,” Blunt told ABC’s George Stephanopoulos on “This Week” today when asked whether he had any second thoughts on the letter.

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The letter, an effort led by freshman Sen. Tom Cotton of Arkansas, was signed by 47 Republican senators including several potential GOP presidential candidates. It said that an agreement between the U.S. and Iran not ratified by Congress should be considered an executive action any future president could revoke.

Several GOP signees, including Sens. John McCain, R-Ariz., and Ron Johnson, R-Wis., have walked back their support for the tactic after the negative response in Washington and across the country.

But Blunt said the letter was “essentially an op-ed,” expressing the Senate’s role in treaty negotiations.

“There is a constitutional role here for the Senate if you want this agreement to be permanent, binding and long-term,” he said on “This Week.”

When asked whether the letter hurts the administration’s ability to broker further international sanctions against Iran, Blunt said, “No deal is better than a bad deal.

“I think these negotiations have gone in a dramatically bad direction,” Blunt added. Secretary of State John Kerry is set to arrive in Switzerland for the latest round of nuclear negotiations with Iran’s foreign minister Mohammad Javad Zarif.

On Saturday, White House chief of staff Denis McDonough sent a letter to Tennessee Sen. Bob Corker, the Republican chair of the Senate Foreign Relations Committee, warning against congressional action that would interfere with negotiations.

Corker, who did not sign Cotton’s letter, has introduced bipartisan legislation to increase congressional oversight of nuclear negotiations and require the president to submit any nuclear deal to Congress for review and approval.