As President Obama announced sanctions against Russia on Monday, a group of Russian officials arrived in San Francisco for a surprise inspection of the U.S. strategic nuclear arsenal.

The inspections, part of a process agreed to under the 2010 New START weapons reduction treaty, signaled business as usual in at least one area of bilateral cooperation.

The treaty is far from the only arms-control investment between the two countries. Russia and the United States have cooperated on efforts to keep nuclear materials out of terrorist hands, they are jointly negotiating limitations on Iran’s nuclear program, and they have joined in the effort to destroy Syria’s chemical weapons arsenal. …

Russia is key to the nonproliferation agenda, which has been Obama’s signature foreign policy initiative. Asked Friday whether Moscow intends to remain cooperative, national security adviser Susan E. Rice said, “We haven’t seen any evidence to the contrary.”