BACKSTORY At a Little Rock restaurant, after Mr. Clinton was elected president, Emanuel ticked off a list of disloyal Democrats and other political enemies, stabs the table with his knife screaming, ''Dead!'' ''Dead!'' ''Dead!'' after each name. Seven months after moving into the West Wing as Obama's COS, Emanuel is emerging as perhaps the most influential White House COS in a generation. But with his prominence in almost everything important going on comes a high degree of risk. As the principal author of Mr. Obama’s do-everything-at-once strategy, he stands to become a figure of consequence in his own right if...