A letter sent by 47 Republican senators to Iranian leaders in defiance of President Barack Obama is a civics lesson, not the act of traitors, said Arkansas Senator Tom Cotton, the freshman Republican who drafted the message.

“We’re making sure that Iran’s leaders understand if Congress doesn’t approve a deal, Congress won’t accept a deal,” Cotton, 38, whose letter evoked a sharp rebuke from the White House, said Tuesday on MSNBC’s “Morning Joe” program. “Because we’re committing to stopping Iran from getting a weapon.”

Obama, Vice President Joe Biden and other Democrats excoriated the letter’s authors Monday, saying Republican leaders were reaching out to a U.S. adversary to try to undermine the president. The front page of the New York Daily News Tuesday put images of Cotton and other Senate Republicans with the headline “Traitors.”

Asked whether the signatories were traitors, Cotton replied negatively and said they were just trying to speak for the American people.

Cotton’s open letter addressed to the leaders of the Islamic republic warned that any agreement they struck with Obama on their nuclear program may be reversed by his successor or changed by lawmakers in the U.S.

“This letter, in the guise of a constitutional lesson, ignores two centuries of precedent and threatens to undermine the ability of any future American president, whether Democrat or Republican, to negotiate with other nations on behalf of the United States,” Biden said in a statement Monday.

‘Wrong Decisions’

Cotton shot back Tuesday.

“Joe Biden, as Barack Obama’s own secretary of defense has said, has been wrong about nearly every major foreign policy and national security decision in the last 40 years,” he said.

The back-and-forth between Republicans in Congress and the White House comes as the Obama administration faces an end-of-month deadline on a deal to limit Iran’s nuclear program.

Obama and White House officials have said the likelihood of reaching a deal is no more than 50 percent.

Republicans, including Cotton, have said Congress should have the final say on the deal, a proposal Obama has rejected.

Disarmament Sought

Cotton said any deal with Iran should force total disarmament of the nation’s nuclear program. If Iran doesn’t agree, the U.S. should be willing to use military force, he said.

“I think we have to have a credible threat of military force on the table,” he said.

Cotton’s letter came about a week after Israeli Prime Minister Benjamin Netanyahu, appearing at the invitation of Republican House Speaker John Boehner and without consulting the White House, used an address to Congress to warn against a deal with Iran.

Asked about Obama’s statement that Republicans were trying to “make common cause with hardliners in Iran,” Cotton said the reputation of Iranian leaders is why they should not be allowed to develop a nuclear weapon.

“There are nothing but hardliners in Tehran. They’ve been killing Americans for 35 years. They killed hundreds of troops in Iraq,” he said. “If they do all those things without a nuclear weapon, imagine what they’ll do with a nuclear weapon.”

(A previous version of this story corrected the wording of Cotton’s comment in the second paragraph.)