Obama swamps Clinton on Pennsylvania airwaves

Barack Obama is vastly outspending Hillary Clinton so far on Pennsylvania's airwaves leading up to the crucial April 22 primary.

By some counts, he is buying five times more air time than Clinton. Thus far, the TV ads have mostly been biographical. One features a snippet of his speech at the 2004 Democratic National Convention in Boston, where he burst on to the national stage, plus testimonials from a Republican and Democratic leader in the Illinois legislature about his record there.

The $2 million in ad buys could help partly explain why Obama, who is in the middle of a bus tour across the Keystone State, is closing the gap in the polls to the low double digits. Governor Ed Rendell, Clinton's biggest-name supporter in the state, predicted on CNN this afternoon that she would win -- but probably not by as big a margin.

Obama also outspent Clinton in Ohio, but she won the Buckeye State on March 4 to revive her candidacy. But by holding down the size of a Clinton victory in Pennsylvania, Obama could preserve his edge in both total delegates and total popular vote.