As President Obama prepares to launch his 2012 re-election campaign, one of his top advisers admits they have no idea who might be his ultimate GOP opponent. 'This is most unfathomable Republican field in my lifetime," Obama political adviser David Axelrod tells USA Today. "I don't think anybody in the media or in either party can tell you with any degree of certainty who the Republican nominee will be." But Axelrod, who left the White House last week to begin working for the campaign, went out of his way to praise one of Obama's potential rivals, Mitt Romney. The former...