Last week, in an unprecedented political move, 47 U.S. Senators sent a public letter addressed to the leadership of Iran, promising to oppose and undermine American negotiations with that country. Our diplomats are in the final stages of securing an agreement that would prevent Iran from getting a nuclear weapon. This obvious effort by some members of Congress to undercut national security policy is not only unconstructive and embarrassing—it is irresponsible.

As a veteran, and like a clear majority of Americans, I support negotiations that have a real chance of keeping America and her allies safe and preventing another uncertain war in the Middle East. You should too.

The Senate has a vital role to play in foreign policy, but this isn’t it. Congress’s hard work in passing bipartisan sanctions against Iran–along with the administration’s work to rally the international community to the cause–set us up for success and brought Iran to the table. That is what smart and successful foreign policy looks like: America presenting a united front to friends and adversaries around the world. When small groups of senators act on their own to publicly oppose tough diplomacy, America looks weak and divided.

That appearance of weakness and division is not the only danger. Any in Congress who oppose a negotiated outcome without proposing serious alternatives could be pushing us closer to war. Our military leaders have already told us that there is no military-only outcome that can prevent Iran from getting a nuclear weapon. After all, we could physically strike specific facilities in Iran, but how can we bomb away a country’s understanding of nuclear science? Security experts agree that Iran would only accelerate their efforts to build a nuclear weapon. Even the threat of war could prompt Iran to bolster its defense capability in order to defend against American attacks.

American diplomats know all too well the danger Iran poses to American security and our allies around the world, and they have been working tirelessly to keep nuclear weapons far out of Iran’s reach. This tough diplomacy has already made us safer: Iran’s nuclear program has been frozen for more than a year. International inspectors have unprecedented access to Iranian facilities. The administration is unified in its promise to “distrust and verify,” and have based any progress during negotiations on routinely requesting verifiable evidence that Iran isn’t cheating. The political stunt that occurred last week threatens to undo all that we have achieved, and genuinely puts American security at risk.

Congress has an important role to play in overseeing national security, but Senators should not micromanage our generals deployed to the battlefield; they must not do so for American diplomats during the final stages of nuclear negotiations. The stakes are just too high. Undermining official American foreign policy in action endangers us all and irresponsibly takes diplomacy off the table just when it could be successful.