In 1799, the Logan Act made it a felony for any US citizen to carry out direct correspondence with a foreign government “in relation to any disputes or controversies with the United States, or to defeat the measures of the United States.”

Despite never being successfully used, the law is still on the books, and is getting a look in the wake of yesterday’s letter by Sen. Tom Cotton (R – AR), and signed by 46 other Republican senators addressed to the Islamic Republic of Iran.

The letter warns Iran against agreeing to a nuclear deal with the Obama Administration, on the grounds that a future US Congress or US President would dishonor the deal, saying they won’t consider any deal made by the president as a real deal with the United States because they oppose the deal.

The Senate has unsuccessfully been trying to kill the talks for months, either by getting a “veto power” over the terms of any final deal, and failing that to try to impose some sanctions in explicit violation of the interim treaty in hopes of scaring Iran away.

Iranian Foreign Minister Javad Zarif dismissed the comments, saying that international law was very clear about treaties being binding and that Iran is treating the letter as a “propaganda ploy” trying to sabotage diplomacy, which of course is exactly what it is.

It is unprecedented for officials to do something like that, and has fueled talk of violation of the Logan Act, and indeed even treason as an open attempt to circumvent the White House’s ongoing efforts as part of the P5+1 to make a deal.

For legislators, having failed to undermine diplomacy through acts of Congress, warning a diplomatic partner of their intended duplicity is certainly a novel situation, but it is unlikely that any legal censure will result from it.

And whatever else you can say about the Republican senators in this case they’re not lying. They’re definitely not to be trusted in upholding diplomatic deals, and at the behest of the Israeli lobby, sooner or later they’ll probably dishonor any treaty reached with Iran.

It is interesting to note that in the past several decades the only talk of using the Logan Act has always been against people “interfering” by trying to make peace when an administration was trying to make war. In this case, the administration is seeking a peaceful rapprochement, and the “interfering” is trying to undermine that.