New York City Mayor Michael Bloomberg acknowledges applause during the U.S. Conference of Mayors 81st winter meeting in Washington, Friday, Jan. 18, 2013. At left is U.S. Conference of Mayors President. Philadelphia Mayor Michael Nutter (AP Photo/Manuel Balce Ceneta)

Associated Press
New York City Mayor Michael Bloomberg acknowledges applause during the U.S. Conference of Mayors 81st winter meeting in Washington, Friday, Jan. 18, 2013. At left is U.S. Conference of Mayors President. Philadelphia Mayor Michael Nutter    (AP Photo/Manuel Balce Ceneta)
New York City Mayor Michael Bloomberg acknowledges applause during the U.S. Conference of Mayors 81st winter meeting in Washington, Friday, Jan. 18, 2013. At left is U.S. Conference of Mayors President. Philadelphia Mayor Michael Nutter (AP Photo/Manuel Balce Ceneta)