An already heated battle between the White House and Republicans over negotiations to curtail Iran’s nuclear program grew more tense when 47 Republican senators sent a letter to Iran designed to kill any potential deal. But is it treason? (Jason Aldag/The Washington Post)

An already heated battle between the White House and Republicans over negotiations to curtail Iran’s nuclear program grew more tense Monday when 47 Republican senators sent a letter to Iran designed to kill any potential deal.

The White House responded by accusing the Republicans of conspiring with Iranian hard-liners, who oppose the delicate negotiations, and suggesting that their goal was to push the United States into a military conflict.

“I think it’s somewhat ironic to see some members of Congress wanting to make common cause with the hard-liners in Iran,” President Obama said a few hours after the letter was made public. “It’s an unusual coalition.”

Vice President Biden blasted the letter as “beneath the dignity of an institution I revere.”

“In 36 years in the United States Senate, 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,” Biden said in a statement.

The letter, written by Sen. Tom Cotton (R-Ark.), suggests that any deal between Obama and the Iranian leadership would amount to only an “executive agreement” that could be undone by Congress or a future president. “The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms of the agreement at any time,” states the letter which was first reported by Bloomberg View.

The Republican signatories dismissed Obama’s assertion that they are cozying up to Iranian hard-liners.

“I think that’s a laughable charge coming from this administration,” said Sen. Dan Sullivan (R-Alaska), who signed the letter. He said the administration’s rush to secure a deal with Iran had led it to dismiss Congress’s concerns.

Administration officials insisted that the president doesn’t need congressional approval to make a deal with Iran and that Congress wouldn’t be able to alter the terms of a deal. “There are several inaccuracies in the letter about how things work,” said State ­Department spokeswoman Jen ­Psaki.

Iran’s foreign minister, meanwhile, dismissed the letter as “mostly a propaganda ploy.”

The Republican outreach to Tehran’s leaders comes at a critical juncture in the negotiations over Iran’s nuclear program. Obama has said that Iran must agree to the outline of an accord by the end of March or further talks would be pointless.

It also comes only a week after Israeli Prime Minister Benjamin Netanyahu denounced the Obama administration’s nuclear negotiations in a rousing speech before a joint meeting of Congress. Netanyahu spoke at the invitation of House Speaker John A. Boehner (R-Ohio), who didn’t consult with the White House or Democrats in Congress before issuing the invitation.

Senate Minority Leader Harry M. Reid (D-Nev.) criticized a letter signed by 47 Senate Republicans warning Iranian leaders against negotiations with the Obama administration, saying the letter "is the kind of pettiness that diminishes us as a country." (C-SPAN)

[Netanyahu says U.S. is on verge of ‘bad deal’ with Iran over nuclear program]

The White House derided that invitation as a breach of protocol designed to undercut the president’s ability to conduct foreign policy. On Monday, White House press secretary Josh Earnest described Cotton’s letter as a “continuation” of a partisan strategy designed to push the United States into a military conflict with Iran that would, at best, delay the Iranian program for only a few years.

“The rush to war or at least the rush to the military option that many Republicans are advocating is not at all in the best interest of the United States,” he said.

The deal being negotiated with Iran would limit its capacity to enrich uranium to the point that, if Iranian leaders decided to kick out inspectors, it would take the country at least a year to produce enough fuel for a bomb.

Iran would also have to commit to intrusive inspections by the International Atomic Energy Agency over the course of the agreement. The United States initially asked Iran to agree to limitations on its nuclear program lasting 15 to 20 years, but Tehran has pressed for a shorter period.

Obama has suggested in recent days that a deal could be imminent. “I think it is fair to say that there is an urgency because we now have been negotiating for well over a year,” he said in an interview with CBS News that aired Sunday.

If Iranians agree to the deal and abide by the inspections regime, the White House could start to ease economic sanctions, which have crippled Iran’s economy, in the coming months and years. Lifting all American sanctions on Iran would require congressional action.

Cotton, an Iraq war veteran and national security hawk, characterized his letter as a remedial civics lesson designed to educate Iran’s mullahs on the limits of presidential power. “Many Iran experts say that Iran’s leaders don’t understand our Constitution,” Cotton said in an interview with Fox News Channel.

Cotton tweeted his letter at Iranian officials and encouraged Democrats, including presumptive presidential front-runner Hillary Rodham Clinton, to add their signatures.

“We already have four senators on the letter who were thinking about running for president,” said Cotton, who later added: “I’ve spoken privately with other presidential candidates who might join us.”

[Who is Tom Cotton?]

The letter drew widespread derision from Democrats, who blasted it as an amateurish attempt to torpedo the negotiations.

“This is not a time to undermine our commander in chief purely out of spite,” Senate Minority Leader Harry M. Reid (D-Nev.) said Monday afternoon in an impassioned 10-minute speech attacking the Republican intervention. “We should always have robust debate about foreign policy, but it’s unprecedented for one political party to directly intervene in an international negotiation with the sole goal of embarrassing the president of the United States.”

Other Democrats agreed. “This letter only serves one purpose — to destroy an ongoing negotiation to reach a diplomatic agreement in its closing days,” said Sen Dianne Feinstein (Calif.), the ranking Democrat on the Senate Intelligence Committee.

Rep. Adam B. Schiff (Calif.), the ranking Democrat on the House Intelligence Committee, said in a tweet that he was “beyond appalled” by the letter.

It’s unclear what impact the letter will have on the delicate negotiations.

Some prominent Republicans, including Sen. Bob Corker (R-Tenn.), the Senate Foreign Relations Committee chairman, declined to sign Cotton’s letter. An aide to the senator said he’s focused on building support for a bipartisan bill that would require Congress to review any nuclear agreement with Iran. The president has said he would veto such a bill.