As you have no doubt heard by now, 47 Republican senators wrote an open letter directed at Iran’s leadership. Its main message:

We will consider any agreement regarding your nuclear-weapons program that is not approved by the Congress as nothing more than an executive agreement between President Obama and Ayatollah Khamenei. … The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms of an agreement at any time.

It almost beggars belief a member of the U.S. Senate — much less almost half — would try to pull the rug out from a presidency in the midst of sensitive negotiations with another state. More from Reuters:

The executive branch is responsible for negotiating international agreements and lawmakers rarely intervene directly with the leaders of another nation while the president’s administration is negotiating a pact.

Few precedents exist in American history. In the New York Times, Peter Baker wrote:

The White House and congressional Democrats expressed outrage, calling the letter an unprecedented violation of the tradition of leaving politics at the water’s edge. Republicans said that by styling it as an “open letter,” it was akin to a statement, not an overt intervention in the talks.

“It’s somewhat ironic to see some members of Congress wanting to make common cause with the hard-liners in Iran,” Mr. Obama told reporters. “It’s an unusual coalition.”

In fact it’s a bridge too far even for some who are anti-Iran. The New York Daily News ran this headline on its front page under pics of McConnell, et al: “Traitors.” From its editorial, in which it first felt compelled to say that Iran’s leaders “may be murderous zealots”:

We join GOP signatories in opposing the pact as outlined, but we strenuously condemn their betrayal of the U.S. constitutional system.

… 47 Republican U.S. senators engaged in treachery by sending a letter to the mullahs aimed at cutting the legs out from under America’s commander-in-chief.

…. [They] represented the bulk of the Republicans’ 54-member senatorial majority, vesting their petulant, condescending stunt with the coloration of an institutional foreign policy statement.

They are an embarrassment to the Senate and to the nation.

It almost seems like a pincer attack by the Republicans to sabotage President Obama’s policymaking, in tandem with King v. Burwell, the lawsuit before the Supreme Court intended to roll back the Affordable Care Act, on the domestic front.

Iranian Foreign Minister Mohammad Javad Zarif saw right through the letter.

“In our view, this letter has no legal value and is mostly a propaganda ploy. … It is very interesting that while negotiations are still in progress and while no agreement has been reached, some political pressure groups are so afraid even of the prospect of an agreement that they resort to unconventional methods, unprecedented in diplomatic history.”

Meanwhile, legal expert Peter Spiro at Opinio Juris  thinks the letter may be a violation of the Logan Act, the federal law that forbids unauthorized citizens from negotiating with foreign governments.

Most putative Logan Act violations violate the spirit and structural foundations of the Logan Act (John Boehner’s invitation to Benjamin Netanyahu supplying a recent example). This one seems to squarely satisfy its elements. We have:

a correspondence with a foreign government (whether direct or indirect, in the form of an “open letter”, matters not),

without the authority of the United States (it enjoys no imprimatur from the executive branch nor, for that matter, from Congress as an institution),

with the pretty clear intent “to influence the measures or conduct of” the government of Iran in relation to a controversy with the United States.

Though prosecution is unlikely, it doesn’t hurt to sign this petition that someone started at WhiteHouse.gov:

File charges against the 47 U.S. Senators in violation of The Logan Act in attempting to undermine a nuclear agreement.

One can’t help but conclude that just when Republicans step back from the edge of the cliff as a Jeb Bush presidential candidacy gains traction, they just can’t help themselves and race back toward the cliff.