The announcement yesterday that Marine Gen. John Allen will retire instead of becoming the supreme allied commander of NATO immediately raises a question: Who will head to Brussels instead? Foreign Policy reported on its E-Ring blog that names being floated for the NATO job include Marine Gen. Gen. Jim Amos, commandant of the Marine Corps. The Daily Beast had a similar report last week, before Allen’s decision to retire was announced. Could Amos really move on, though? A shift like that would be a shock in the Corps, which Amos has led since October 2010 through a time filled with…