**FILE** In this file photo from Jan. 30, 2007, Sen. John McCain, R-Ariz., left, and Sen. Barack Obama, D-Ill. greet on Capitol Hill in Washington prior to testifying before the Senate Environment and Public Works Committee a hearing on global warming. Barack Obama, the Democratic presidential hopeful, has pivoted into a general-election fight against the certain Republican presidential nominee, John McCain, without waiting for the Democratic marathon to end. (AP Photo/Dennis Cook)