Forty-seven irresponsible Republican senators made a political and diplomatic mistake sending an “open letter” to the theocracy ruling Iran regarding nuclear-weapons negotiations.

“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 stated.

Politically, the stunt increases the likelihood that Democrats will rally around the president, just as they did after the insulting breach of protocol that led to Israeli Prime Minister Benjamin Netanyahu’s address to Congress last week. Democrats likely will close ranks, even though many agree with their GOP colleagues that they should get to vote on any agreement.

The letter was drafted by Arkansas Republican Tom Cotton, who has been in office all of two months. It sets a terrible precedent that a president can be undermined during diplomatic negotiations. That could make it less likely that future executives — including presumptive presidential candidates Marco Rubio, Rand Paul, Ted Cruz and Lindsey Graham, who each signed the letter — will be trusted by allies and adversaries alike to be able to deliver on negotiated agreements.

Diplomatically, the letter seems oblivious to the fact that the negotiations aren’t bilateral, but multilateral through the P5+1 process (five permanent members of the U.N. Security Council and Germany). These nations, along with others, have imposed unusually successful sanctions on Iran, which is the only reason a deal may actually happen. The 47 senators seem to be blithely ignoring necessary perspectives from London, Paris, Berlin, Beijing and Moscow, as well as other capitals influenced by these powers. If Iran is able to claim that it was Washington, not Tehran, that torpedoed the talks, the sanctions regime may well unravel without Iran having to compromise on its nuclear program.

If so, the next step could include military action, which could spiral into yet another major Mideast war. The GOP senators should be as blunt about this possibility as they are about their opinions on Obama’s diplomacy.