IT’S BEEN 21 / 2 months since President Obama nominated the senior Russia director on his National Security Council staff, Michael A. McFaul, to be U.S. ambassador to Moscow. If you’ve been following how well Washington works these days, it may not surprise you to learn that Mr. McFaul has yet to take up residence in Spaso House.

But in the annals of Washington dysfunction, this delay merits a moment of attention, because Mr. McFaul has been acknowledged, pretty well universally, to be an excellent choice for the ambassadorship. Mr. McFaul, a Stanford University professor and Hoover Institution scholar before entering government, is one of the nation’s leading experts on Russia. He has been a proponent of democracy and human rights in that country since Soviet days. In these partisan times, he enjoys unusual support from the foreign policy establishments of both parties.

Nonetheless, a single senator, Republican Mark Kirk of Illinois, is holdingthe nomination hostage in a dispute with the administration about the possibility of U.S.-Russian cooperation in anti-missile defense. The two nations have talked about that prospect with respect to the growing threat from Iran, and Mr. Kirk fears it could lead to the transfer of U.S. military secrets to Russia — and through Russia potentially even to Iran.

We sympathize with the senator’s suspicions of Russian-Iranian ties. But we think he’s picked an odd moment and an odd target for this fight. An odd moment because, far from cooperating, the Russians lately have been threatening to bomb U.S. anti-missile sites; any prospect of sharing technology seems remote. And the wrong target, because Mr. McFaul is as clear-eyed about the nature of the Vladi­mir Putin regime as any envoy likely to be nominated by this or any other administration. In fact, the only people who might be perturbed by his confirmation are Russian officials, who know that Mr. McFaul will not be fooled by their pseudo-democracy.

White House spokesman Tommy Vietor says the administration never has shared sensitive information about anti-missile technology with the Russians and has no intention of doing so. But the kind of blanket promise Mr. Kirk seeks would bind this and future administrations in a way no White House could accept, he says.

Assuming he appoints someone qualified, Mr. Obama, like all presidents, is entitled to the ambassador of his choice. Republicans wary of the Putin regime ought to welcome an ambassador like Mr. McFaul, someone who can capably interact with — and, if necessary, stand up to — that regime, and who understands the importance of reaching out simultaneously to Russian civil society.

Given those shared interests, you’d think they could work something out.