When Mitt Romney strode across the the platform Friday evening and took his place behind a podium in front of the largest crowd he's drawn this year, he sounded familiar stump speech themes of bipartisanship and economic recovery. But the parade of high-profile surrogates who opened for the candidate fixated on another, more explosive issue — one with a particular power to both animate conservatives, and frighten Romney's senior staff. For about 60 minutes before Romney took the stage, Topic A was Libya. Ever since terrorists stormed the U.S. Consulate in Benghazi in September — killing four Americans, including the...