FILE - This Sept. 25, 2012 file photo shows White House senior adviser Valerie Jarrett, left, talking with singer William Adams, also know professionally as Will.i.am, at the Clinton Gl

 

              FILE - This Sept. 25, 2012 file photo shows White House senior adviser Valerie Jarrett, left, talking with singer William Adams, also know professionally as Will.i.am, at the Clinton Gl
FILE - This Sept. 25, 2012 file photo shows White House senior adviser Valerie Jarrett, left, talking with singer William Adams, also know professionally as Will.i.am, at the Clinton Global Initiative Annual meeting in New York. Whatever their political beliefs, some artists perform an age-old ritual: warming up the crowd before a political rally, generating enthusiasm and all-important buzz for events that otherwise could be overlooked in a crowded news cycle. For politicians _ even those as well known as President Barack Obama and Republican presidential candidate, former Massachusetts Gov. Mitt Romney _ celebrity warm-up acts can provide validation by taking them out of the political realm into popular culture, said Darrell West, director of governance studies at the Brookings Institution think tank in Washington. (AP Photo/Pablo Martinez Monsivais, File)