Rahm Emanuel quits Chicago, but can the Democratic Party quit him?

On Tuesday, incumbent Chicago Mayor Rahm Emanuel issued a surprise announcement: He would not, as many expected, seek a third term as mayor of Chicago. The shock announcement prompted radically different reactions. Working-class locals largely rejoiced at the news. The local business press, on the other hand, wore their frowns so tight that they risked pulling a muscle.

But while Emanuel may be retreating from public service after almost three decades, it remains an open question as...