President Vladimir Putin on Tuesday formally lowered the threshold for Russia’s use of its nuclear weapons, a move that follows U.S. President Joe Biden’s decision to let Ukraine strike targets inside Russian territory with American-supplied longer-range missiles. The new doctrine allows for a potential nuclear response by Moscow even to a conventional attack on Russia by any nation that is supported by a nuclear power. Russia’s Defense Ministry said Ukraine fired six U.S.-made ATACMS missiles early Tuesday at a military facility in Russia's Bryansk region that borders Ukraine, adding that air defenses shot down five of them and damaged one...