U.S. national security adviser Jake Sullivan says Ukrainian efforts to join NATO should be taken up "at a different time," throwing cold water on the country's desire to join the international alliance and potentially easing Russian tensions as President Vladimir Putin has begun accelerating rhetoric of potential nuclear war. Ukraine formally applied to join NATO as a military partner on Friday, coinciding with Putin's announcement that Russia would be formally annexing four occupied regions within Ukraine's borders. If accepted, NATO-aligned forces would formally be drawn into the war, pitting forces in the West against the Russian military and, potentially, escalating...