In a new open letter, three dozen retired US generals and admirals have endorsed the P5+1 nuclear deal with Iran as the “most effective means” to prevent Iran from acquiring a nuclear weapon, and called on Congress to vote in favor of the pact.

The letter echoes sentiment from current Joint Chiefs of Staff chairman Gen. Martin Dempsey, who said that resolving the dispute with Iran diplomatically “is superior than trying to do that militarily.”

A military confrontation with Iran is very much the point for a lot of the Congressional opponents, however, and the letter also seemed aimed at them, saying that a US war with Iran would be much easier to sell internationally if the diplomatic deal had been tried first.

Congress is not expected to be able to muster enough votes to block the deal, and administration officials are warning that if they do it would be calamitous for America’s global standing, and making diplomacy with other nations much more difficult in the future.