When the P5+1 revealed to the world the dubious outlines of a prospective nuclear accord with Iran, one of the many shortcomings observers lamented was the concession that Iran would not be required to roll back its enrichment capabilities or dismantle any of its nuclear facilities. The most troubling facility that will remain intact is the underground enrichment site at Fordow.

Iran did not voluntarily disclose the existence of this facility. Even in spite of Iran’s duplicity, this hardened enrichment site will be allowed to remain intact, and would be transformed from a site devoted to creating fissionable material to a nuclear university. Fear not, the deal’s proponents insisted. The United States still possesses the military capacity to enforce the terms of this deal through force. In essence, the teeth of this arrangement are, as they always were, American military might.

Republicans were concerned by this line of thinking. If the deterrent that would compel Iran to abide by the terms of a nuclear deal was American military force, the political will to go to war with Iran must exist in the United States. Any honest observer of Western politics must concede that it does not. At least, not at the moment.

But a new obstacle to the use of American (or Israeli) force against Iranian facilities has been erected this week in the form of sophisticated Russian surface-to-air missile batteries. In violation of yet another Obama administration “red line,” and in defiance of the terms of the vaunted “reset” in relations with Russia, Moscow recently agreed to end a moratorium on the sale of S-300 missiles to Iran.

The State Department insisted that this development will in no way derail nuclear negotiations with Iran, as if anything could. But experts warn that Russia’s decision to provide Iran with anti-air missile technology could fracture the international community and reduce the capability of the Western powers to punish Iran with force if it deviates from the terms of a nuclear accord.

“Monday’s announcement by Russia flies in the face of this purported diplomatic success and left the Obama administration scrambling to respond,” The Washington Free Beacon’s Adam Kredo reported. “State Department spokeswoman Marie Harf said that while the sale of the S-300 to Iran would not violate United Nations Security Council sanctions on Tehran, it remains a concern to the United States.”

Elliott Abrams, a former White House National Security Council (NSC) member, wrote that the breakdown in the Obama administration’s campaign to block the sale is yet another sign of Washington’s waning influence.

“American ‘red lines’ aren’t what they used to be, Medvedev is gone, and the ‘reset’ with Russia is an embarrassment,” Abrams wrote at the Council on Foreign Relations (CFR). “So is the way the Obama administration claimed credit for changing Russia’s policy toward Iran.”

“From a practical military standpoint, the sale of the S-300 would directly challenge the U.S. position that ‘all options are on the table’ should Iran try to subvert the nuclear deal,” The Daily Beast’s Dave Majumdar wrote. “The addition of the powerful missile defense system would make punitive airstrikes against Iran extremely difficult.”

A senior U.S. Marine Corps aviator said that if Russia delivers the S-300 missile to Iran, it would fundamentally change U.S. war plans. “A complete game changer for all fourth-gen aircraft [like the F-15, F-16 and F/A-18]. That thing is a beast and you don’t want to get near it,” he said.

The sale of the S-300 also would neutralize any possibility that Israel could take unilateral action against Iran, one senior Air Force commander noted. The S-300 would effectively prevent the Israeli air force from attacking Iran until the F-35 is delivered to that nation.

But does the sale of S-300 air-defense missiles to Iran really dramatically reduce America’s or Israel’s ability to effectively strike at Iranian nuclear targets? Some reports suggest that this development is not a game-changer.

“If the Israeli Air Force had the ability to act against Iran’s nuclear facilities before the S-300, then it will have it afterward, too,” retired IAF general Asaf Agmon recently said, according to a Times of Israel report.

He said Russia was unlikely to reveal, in the event of a sale, which system it had provided and that it was Israeli intelligence that would have to deliver that information to the IAF. The S-300 PMU, for example, was sold to Cyprus in January 1997 and, amid Turkish threats of a preemptive strike and even war, transferred to Greece in 2007. Israel, since the deployment of the system in Crete, has conducted several joint operations with the Greek air force. Asked whether Israel had trained against that version of the S-300, he said, “I’d put my money on Yes.”

I’d put more weight on American Air Force sources speaking to reporters on background than I would a retired IAF general blustering on behalf of the Israeli government. It’s highly likely that Russia has blunted the West’s ability to enforce a nuclear arrangement with anything beyond rhetoric.