Anchored by Jake Tapper, The Lead airs at 4 p.m. ET on CNN.
What's the U.S. plan on Russia's "all out" invasion? Plus, a look at the strategy for fighting ISIS.
(CNN) – Russian troops have taken positions in Ukraine's Crimea peninsula, as world leaders scramble to find a solution to this conflict.
Now, moves at sea are also raising the stakes, in a key channel into the Black Sea, a Turkish waterway identified as a world oil transit choke point by the U.S. government.
The Bosphorus Strait was the scene of a tense situation involving a key Ukrainian warship that CNN's Ivan Watson was tailing off the coast of Turkey.