Repairing his country's tattered relationship with Russia has been a priority for U.S. President Barack Obama. That process got a symbolic start in March when Secretary of State Hillary Clinton presented her counterpart, Mr. Sergei Lavrov, with a "reset" button in Geneva. (The moment was embarrassing as the button was mislabeled "overcharge" in Russian.) It picked up in earnest this week as Mr. Obama made his first visit as president to Russia, where he vowed to work toward a new partnership with Moscow. Despite his earnest intentions, it will not be easy.

Relations between Washington and Moscow have deteriorated over the last decade. While there was hope that a shared sense of purpose would bring the two former adversaries together in the aftermath of the Sept. 11, 2001, terror attacks, Russia has felt increasingly marginalized by subsequent U.S. moves. The expansion of NATO toward Russia's borders, the U.S. decision to proceed with the installation of a missile defense system in former Soviet satellites, Western support for governments, most notably Georgia's, that deliberately antagonized Russia, and the lack of progress on Moscow's bid to join the World Trade Organization all contributed to a sense in Russia that the U.S. saw Moscow as a rival rather than a partner.

The U.S. has its own list of complaints. Russian behavior in Georgia is exhibit one, but Moscow's failure to do more to stop Iran's nuclear program, its incessant complaints about U.S. power, its role in the Shanghai Cooperation Organization decision to call for the removal of U.S. forces from Central Asia, and Russia's more muscular and assertive foreign policy — which often seems intended to blunt U.S. initiatives — top an equally long bill of particulars.

Mr. Obama had two days to reframe the relationship and to do that he had to address both the tone of the relationship and the agenda itself. The first part was relatively easy. He spoke of Russia as a partner that works with the U.S. and other nations to find solutions to shared problems. As Mr. Obama explained in a speech to the New Economic School in Moscow, "America wants a strong, peaceful and prosperous Russia." For him, "the pursuit of power is no longer a zero-sum game — progress must be shared."

In his speech at the school as well as by his visit to the Tomb of the Unknown Soldier — his first stop in Moscow — Mr. Obama invoked the heroism of Russian sacrifices during World War II and subtly recalled a time when the U.S. and Russia worked together for common purposes. Substance must now follow.

Mr. Obama and Russian President Dmitry Medvedev reached an understanding on the outline of a deal for cuts in nuclear arms, agreed to permit U.S. military shipments to Afghanistan via Russian land and airspace, and decided to jointly assess the threat posed by Iran's and North Korea's nuclear programs. The big issues defied resolution, however.

Missile defense continues to be a source of real disagreement. Mr. Obama acknowledged that the subject is "a point of deep concern and sensitivity" to Russia, but insisted that the program as envisioned would have no impact on Russian strategic capabilities. Mr. Medvedev noted that the strategic arms understanding notes the linkage of offensive and defensive systems, which he considers a step forward. For him, it signals U.S. recognition of Russia's vulnerabilities and that cuts in strategic systems require Washington to rethink its missile defense plans. Significantly, however, the Russian president never mentioned the word Iran, an indication of the differences in perspective that shape the two leaders' thinking.

We welcome the new tack in this bilateral relationship, but it is important that the U.S. administration be alert to the ripple effects of its dealings with Russia. Moscow is a great power, one that demands respect. But respect for its concerns does not require excessive accommodation. For example, we welcome cuts in nuclear stockpiles, but the credibility of the U.S. extended deterrent must not be affected. This is not a concern that Moscow shares. Moscow and Washington should now move to bring the other nuclear weapons states into multilateral talks to ensure that U.S. and Russian reductions do not embolden other nations to build up their own arsenals.

Similarly, discussions of the viability of missile defense in Europe must not compromise security in Asia, nor should they send the signal to China that such systems — especially those of allies — are negotiable.

Russians need to be convinced of Mr. Obama's good intentions. That requires work. A recent survey showed that only 23 percent of them believe that the U.S. president will do the right thing when it comes to international affairs; sadly, that is nearly twice the number of those who think the U.S. treats Russia fairly. But the burden does not rest on the U.S. shoulders alone. Russia too must step up, doing its share to help solve problems. That is, after all, how a real partnership works.