Barack Obama's campaign will start airing an ad in battleground states today highlighting John McCainJohn Sidney McCainBill Maher delivers mock eulogy for Trump Hillary Clinton roasts NYT's Maureen Dowd over column CNN's Ana Navarro to host Biden roundtable on making 'Trump a one-term president' MORE's recent assertion that the fundamentals of the U.S. economy are strong.

The Obama campaign attacked McCain over the statement yesterday on the campaign trail and in TV appearances by surrogates. Today's ad asks viewers: "How can John McCain fix our economy if he doesn't understand it's broken?"

McCain has consistently asserted, throughout the campaign, that the U.S. economy is fundamentally strong. Democrats have renewed their criticism of the claim after McCain made it again yesterday, the same day the stock market was thrown into turmoil by the collapse of investment bank Lehman Brothers and the sale of financial firm Merrill Lynch.