Sen. Tom Cotton (R-Ark.) (AP Photo/Danny Johnston) Sen. Tom Cotton (R-Ark.) (AP Photo/Danny Johnston)

Even by congressional Republican standards, the naysaying letter to Iran sent Monday by 47 GOP senators was grossly irresponsible. Not only did it undercut President Obama’s ability to negotiate a diplomatic agreement, but it also undermined the aspect of the Iran nuclear deal that would potentially be most beneficial to the United States and Israel.

From the beginning of the Iran nuclear talks, a key U.S. goal has been to obtain an agreement whose duration is long enough that it will bind Iran’s actions into the next generation of leaders that will follow Supreme Leader Ali Khamenei, who is 75 and ailing. Israeli Prime Minister Benjamin Netanyahu stressed the future expiration of the agreement as a key worry during his speech criticizing the deal last week to Congress.

The political wrecking ball that is the Republican caucus has, perhaps unwittingly, challenged precisely this goal of a long-term deal by advising the Iranian leadership that the deal being negotiated is merely an “executive agreement” that could be abandoned if the domestic political winds change. “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,” the letter says.

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)

To this assertion of the impermanence of an agreement, Khamenei and other hard-liners might well respond with an Iranian version of “Amen.” Indeed, they could use the Senate GOP letter as a rationale for abandoning aspects of the deal they find too constraining. That would force the United States to consider military action. The casus belli, bizarrely, might begin with an argument made by Senate Republicans.

“I think it’s somewhat ironic to see some members of Congress wanting to make common cause with the hard-liners in Iran,” Obama told reporters. That was putting it mildly. A blunter assessment came from Rep. Adam Schiff (Calif.), the top Democrat on the House Intelligence Committee, who said he was “beyond appalled” by what the Senate letter-writers had done.

Iranian Foreign Minister Javad Zarif, who doesn’t want hard-liners in Washington or Tehran to upset his dealmaking, responded with a civics lesson of his own: “The authors may not fully understand that in international law, governments represent the entirety of their respective states….Change of administration does not in any way relieve the next administration from international obligations undertaken by its predecessor in a possible agreement about Iran’s peaceful nuclear program.” Whether such views are binding on Khamenei & Co. is a key issue for the future.

This latest GOP tactic of conveying skepticism about the accord directly to Tehran follows House Speaker John Boehner’s invitation last week to Netanyahu to, in effect, lobby against the deal from the floor of the U.S. Congress. These actions may be seen by allies abroad not just as a gesture of contempt for Obama, but also for the broader P5+1 negotiating group that includes Britain, France, Germany, Russia and China.

Liberal bloggers were arguing that the GOP letter violated the Logan Act, named for a Pennsylvania politician’s attempt to meddle in President John Adams’s delicate negotiations with France in 1798. The language of that 216-year-old statute does sound eerily pertinent: “Any citizen…who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government…to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both.”

The Obama administration surely isn’t going to take its GOP critics to court. But this latest gesture of congressional defiance should make reasonable Republicans wonder whether their party’s foreign policy agitprop has moved beyond being merely partisan to downright dangerous.

By sending a letter to Iran, did Republican senators go too far?

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