The White House claimed a key victory Wednesday in its effort to create momentum toward sanctions against Iran for its pursuit of nuclear weapons, saying that comments by Russian President Dmitry Medvedev after a meeting with President Obama represented a shift toward favoring punitive action… Michael McFaul, the president’s top Russia adviser, called Mr. Medvedev’s statement on Iran “a very big change in [Russia’s] position.” He said that the administration’s decision last week to drop a missile-defense plan that had angered the Kremlin had increased the odds of a change.