Russia said Wednesday it was returning more troops and weapons to bases, yet another gesture apparently aimed at easing fears it is planning to invade Ukraine, even as the U.S. said the threat of an attack remained. On Wednesday, the Russian Defense Ministry released a video showing a trainload of armored vehicles moving across a bridge away from Crimea, the Black Sea peninsula that Russia annexed from Ukraine in 2014. It said the movement was part of a return of forces to their permanent bases. A day earlier, the ministry reported the start of a pullback of troops following military...