David Vitter's madam troubles – play-for-pay companions in two cities, it appears today (with a Larry Flynt press conference to pile on tonight), will not force him to resign, but they may help Democrat Mary Landrieu in her re-election bid  next year. Landrieu was one of two endangered Democratic senators in he 2008 cycle (Tim Johnson of South Dakota the other, if he runs again).  With the departure of about half of New Orleans’ residents, demographic changes alone (loss of many black voters) could have resulted in her defeat (Landrieu has won two races very narrowly).