Unconfirmed reports of a secret side agreement to the New START nuclear arms treaty started circulating in mid-October. The side agreement supposedly restricts the U.S.’s ability to pursue a robust missile defense.

The reports drove a number of U.S. Senators to write Secretary of State Hillary Clinton, demanding that the administration make available all the documents and records regarding any side negotiations. Administration officials turned over “summary” documents only, vehemently denying that any side deals were in the works.

Yesterday, the State Department released a fact sheet admitting that the Obama administration has been negotiating with Russia on missile defense “cooperation.” Awkward!

The State Department insists the negotiations weren’t secret. It’s just that they never mentioned it publicly. So that explains THAT.

The sound you hear is that of the administration’s missile defense credibility crumbling. The New START treaty, its protocols and annexes all limit U.S. missile defense options. Don’t just take our word for it. Russian Foreign Minister Sergei Lavrov says so too, insisting that “linkage to missile defense is clearly spelled out in the accord and is legally binding.” Yet the White House continues to assert that the treaty will in no way retard plans to develop and deploy missile defenses. (Something that could be true, provided you have no plans to develop and deploy missile defenses.)

The administration insists the newly revealed negotiations only continue a narrower version of the Defense Technical Cooperation Agreement (DTCA) negotiations undertaken between the Bush administration and Russia, but this time calls it the Ballistic Missile Defense Cooperation Agreement (BMDCA).

“This [BMDCA] agreement shall not constrain or limit the Parties’ respective BMD plans and capabilities numerically, qualitatively, operationally, geographically, or in any other way,” states the fact sheet. But that’s inconsistent with the administration’s formal statement issued when the president signed New START. That statement pledges to the Russians: “The United States missile defense systems are not intended to affect the strategic balance with Russia” — the so-called balance of terror. Therefore it is entirely reasonable to conclude that what the Obama administration calls pursuing missile defense cooperation with Russia is really finding ways to curtail the U.S. missile defense program.

The fact of the matter is that a missile defense system fully capable of defending the U.S. and its allies from non-Russian missiles can’t help but alter the strategic balance with Russia. Conversely, a system that does not affect that strategic balance will leave us and our allies vulnerable to missile attacks from other sources.

No surprise, then, that Bill Gertz reports in The Washington Times that the administration has already agreed to scrap the fourth and final phase of its Phased Adaptive Approach (PAA) for missile defense. That’s the phase intended to give the United States and Europe additional protection against long-range missiles. Scrapping that upgrade is entirely consistent with the formal statement issued by the Obama administration at the time the treaty was signed.

It is now clear that the Senate needs full access to the New START negotiating record to determine what U.S. negotiators were stating during negotiations to the Russians relating to the BMDCA talks. The Senate needs to get to the bottom of the confusion created by today’s fact sheet from State and the earlier U.S. unilateral statement regarding missile defenses.

That’s something that can’t be done in the few days remaining in the lame-duck session. Nor should it be done. As a group of Republican senators-elect noted in a letter to Majority Leader Harry Reid (D-NV), it should be their responsibility — not the lame ducks’ — to consider and vote on this treaty. The treaty is a 10-year contract — one that would become the law of the land and implemented during their watch — after the lame ducks have waddled off the scene. Senators who are leaving office, most by the invitation of the voters in November, lack the necessary democratic mandate to make such a momentous decision.

Owen Graham and Michaela Bendikova work in The Heritage Foundation’s Davis Institute for International Studies.