With midterm elections just about three weeks away, the battle for control of Congress is getting fierce - and ugly.
The Democrats' latest ammo - a new TV ad hitting airwaves this week.
It accuses the U.S. Chamber of Commerce of illegally using foreign money to secretly back Republican candidates.
The chamber denies the claim, saying the money it receives from overseas groups isn't used for political campaigning.
The Obama administration hopes big rallies like this one will help reignite the passion that catapulted Democrats to victory two years ago.
The President will continue stumping for his party in Delaware Friday, and again in Massachusetts Saturday.