Preserving the military option against Iran has long been a key lynchpin of the U.S.’s effort for halting Tehran’s nuclear program. The strategic thinking is obvious: even as the Obama administration attempts to engage Iran diplomatically, it must retain the credible threat of military force so that Iran believes it faces severe consequences if diplomacy fails. Indeed, the only safe way to experiment with soft power — and that is precisely what Obama has been doing — is to reinforce it with the overt possibility of destructive hard power.

Yet yesterday, this strategy collapsed. In his remarks before the Senate Appropriations Committee, Secretary of Defense Robert Gates stated that military action for halting Iran’s nuclear program would be ineffective, and would merely send the Iranian nuclear program further underground. Given Gates’s high rank and bipartisan domestic credibility, this amounts to a virtual declaration that America simply has no military option vis-à-vis Iran whatsoever. After all, how can Obama maintain a military option that his top defense official has declared counterproductive and wasteful?

None of this is to say that Gates’s expert opinion on the viability of the U.S.’s military option against Iran is off-base. Rather, the key point is that Gates’s position on this matter has its appropriate place — behind closed doors. When top policymakers speak openly about the limits of American power, they substantially undermine our credibility to our adversaries. In turn, our adversaries become even less likely to respond to our “soft” overtures.

For this reason, Tehran is now breathing much more easily. With the threat of U.S. military action against it discredited, it stands to lose very little if talks with Washington fail. And insofar as most Iranians support the acquisition of nuclear weapons, negotiations over Iran’s nuclear program are as doomed as ever.