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DENVER — Colorado Sen. Cory Gardner didn’t back down Tuesday as controversy continued to swirl around the letter he and most of his Senate GOP colleagues signed in an effort to undermine a diplomatic breakthrough with Iran to limit that country’s nuclear program.

He also declined to answer more questions about it.

On Monday, Gardner was one of 47 Republican senators including 2016 presidential hopefuls Ted Cruz, Rand Paul and Marco Rubio to sign a letter to Iran’s leaders warning them that they can and will oppose any agreement reached between the U.S., five other countries and Iran.

Colorado Sen. Michael Bennet, a Democrat, blasted Gardner and the Republicans who signed the letter, although not by name, in a statement Tuesday.

“This letter is completely counterproductive and I cannot say enough about the seven Republicans who were wise enough not to sign it,” Bennet said.

Gardner, elected just last November on a promise to be a “new kind of Republican”, sits on the Senate Foreign Relations Committee; the panel’s chairman, Sen. Bob Corker, R-Tennessee, was one of seven more moderate GOP senators who did not sign the controversial letter that has outraged the White House and many foreign policy stalwarts.

Vice President Joe Biden released a strongly worded statement on Monday night, saying that the letter “is beneath the dignity” of the Senate.

“In 36 years in the United States Senate,” Biden said. “I cannot recall another instance in which senators wrote directly to advise another country — much less a longtime foreign adversary — that the president does not have the constitutional authority to reach a meaningful understanding with them.”

According to a press release Gardner’s office sent Monday, the letter is an effort to clarify for Iranian leaders our constitutional system of government, and makes clear that any deal between President Obama and Ayatollah Khamenei that is not approved by the U.S. Congress could easily be modified or revoked in the future.

“I want the leaders of Iran’s regime, the world’s leading state sponsor of terrorism, to know that no deal with the United States will be considered permanent without the approval of the Congress,” Gardner said. “The American people, through their representatives in Congress, will reject any deal that does not completely eliminate the threat of a nuclear Iran.”

Asked for additional comment Tuesday, Gardner’s office stood by its statement from Monday, even amidst new debate in Washington about whether the move, whatever its impact on a potential deal with Iran, is a violation of the Logan Act, which prohibits American citizens from communicating with foreign governments to conduct their own foreign policy.

“It’s a pretty stunning first move for a freshman on the foreign relations committee,” said Matt Chandler, a former deputy chief of staff at the Dept of Homeland Security and now a partner at a homeland security consulting and business advisory firm in Denver.

“Regardless of one’s political proclivity or leaning, its a dangerous precedent and a borderline encroachment on the Logan Act which stipulates the role of foreign affairs to the executive.”

Alan Salazar, chief strategist to Colorado Gov. John Hickenlooper, was even more pointed in a post Monday night on Facebook.

“This action – attempting to sabotage an international agreement – BEFORE it has even been finalized, is worse than contemptible politics. It is a dangerous precedent that undermines the process of conducting foreign affairs,” Salazar wrote. “Let us all hope that this clumsy and reckless behavior by partisan zealots does not become the norm.”

Gardner’s office pointed out Tuesday that, according to the Congressional Research Service at the Library of Congress: “Nothing in section 953 would appear to restrict members of the Congress from engaging in discussions with foreign officials in pursuance of their legislative duties under the Constitution.”

Polis’ ‘Tehran Tom’ tweets draw Republican rebuke

Boulder Congressman Jared Polis, a Democrat, turned his ire over the letter not at Gardner but its primary author, Sen. Tom Cotton of Arkansas, another first-term Republican elected in 2014, firing off a series of tweets labeling the freshman senator and Iraq War veteran “Tehran Tom.”

In response, Republicans have focused on Polis and demanded that he apologize for the tweets.

“Unlike Jared Polis, Sen. Cotton is a decorated war veteran who has put the good of this nation before his own personal ambition time and again,” said Colorado GOP Chairman Ryan Call in a statement Tuesday. “Congressman Polis’s name calling is beneath the office he was elected to, and is another example of why the American people are fed up with Washington politicians.

“Congressman Polis must apologize to Sen. Cotton and the people of Colorado.”