Russia’s movement of the ground-based tactical weapons appeared to coincide with the deployment of U.S. and NATO missile-defense installations in countries bordering Russia. Moscow has long considered the U.S. missile defense buildup in Europe a challenge to Russian power, underlining deep-seated mistrust between U.S. and Russian armed forces despite improved relations between political leaders…

Senior administration officials say New Start, like most arms treaties before it, deals only with strategic nuclear weapons, adding that only after it is ratified can Washington and Moscow begin to negotiate a legally binding, verifiable treaty to limit tactical warheads in Europe.

The positioning of Russian tactical nuclear weapons near Eastern European and the Baltic states has alarmed NATO member-states bordering Russia. They see these as potentially a bigger danger than long-range nuclear weapons. Tactical weapons are easier to conceal and may be more vulnerable to theft, say arms-control experts…

Administration officials say U.S. and Russian negotiators plan to turn their attention to tactical nuclear weapons, as well as larger strategic warheads that aren’t actively deployed, as soon as New Start goes into force. “If we don’t ratify Start, we’re not going to be able to negotiate on tactical nuclear weapons,” one said.