The conference room in the Mountain View, Calif., headquarters of LinkedIn was packed with the stars of Silicon Valley. Top executives of Facebook, Google and Twitter gathered around a table; the billionaire Sean Parker looked on from a back row. The guest of honor: Cory A. Booker, the mayor of Newark. "He's part of this tide," said Gina Bianchini, an entrepreneur who was at the meeting, in May 2009. "It feels like he's one of us." Mr. Booker personally has obtained money for the start-up, called Waywire, from influential investors, including Eric E. Schmidt, Google's executive chairman. A year after...