Democrats are pushing back against the letter, circulated by Sen. Tom Cotton (R-AR) and signed by 47 Senators in all, that warns the Iranian regime that any deal it signs with President Barack Obama could be voided by the next president if it is not ratified by the Senate under the U.S. Constitution. They have enlisted Vice President Joe Biden and even retired Sen. Richard Lugar to disparage the effort. In so doing, they have proved Cotton’s point–and checkmated the administration.

Lugar was a moderate, veteran Senator representing Indiana (though, as it turned out, not really living there) when then-candidate Obama held him up as a model of the kind of Republican he would like to work with. Lugar enjoyed wide respect as an authority on nuclear disarmament, and Obama relied on him to push the New START treaty with Russia through the Senate in 2010, over conservative objections that it gutted missile defense and required lopsided nuclear cuts for the U.S.

The New START treaty was the centerpiece of Obama’s so-called “reset” with Russia, which has since become a complete farce. Not only has Russian President Vladimir Putin annexed the Crimea, invaded the rest of the Ukraine, backed Syrian dictator Bashar al-Assad, and granted refuge to Edward Snowden, but he has also violated New START and other nuclear treaties–even as Obama promised Russia more “flexibility” when freed from accountability to the burdensome electorate.

Part of the reason Lugar lost his primary election to Richard Mourdock in 2012 was because of the weakness of the New START treaty. And yet the Huffington Post drags Lugar out as a weapon against the Cotton effort, proclaiming that Cotton and his colleagues “are not really in the position to formulate legislation and make a serious effort that the president will have to deal with”–a false statement that ignores the Iran Nuclear Agreement Review Act (INARA) that is winning support.

It is certainly unusual to have Senators approach foreign leaders, as Cotton and his colleagues did in tongue-in-cheek fashion, to fight what is a domestic policy dispute. But it is not unheard of for Congress to strike an independent posture on foreign policy–as Democrats did, to their disgrace, in coddling Syria after 2006–and in this case the Senators have no other choice. Obama has refused to listen to Congress on foreign policy–or, in the case of Cuba, even to keep it informed.

The brilliance of the Cotton letter is that it has forced Obama to admit openly what he had only hinted at indirectly before–that he has no intention of submitting any Iran agreement to Congress for ratification–or even for review. That admission exposes the fact that Obama no longer, in any meaningful sense, represents the United States at the negotiating table. That will only add momentum to efforts to override his promised veto on INARA. A freshman Senator has beaten the president.