WASHINGTON — President Barack Obama said Thursday that the 2012 election will be a "fun debate" over two competing visions for the nation, referring to Mitt Romney as the Republican "front-runner" who has backed policies that would undermine middle-class families. At a fundraiser held at a Washington hotel, Obama told supporters that his administration had spent the past three years "cleaning up after some of that mess, and I don't want to have to do it again."