American Bridge 21st Century, a pro-Democrat super PAC founded from liberal watchdog group Media Matters, is campaigning for Mitt Romney to "fire" Donald Trump.

The organization emailed supporters today asking them to pledge "$1 for every day Mitt refuses to Fire The Donald." Last week, American Bridge debuted an ad asking the public to join it in condemning the Romney campaign for its use of celebrity businessman Trump as a fundraiser and supporter given his continued refusal to believe President Obama was born in the United States. Trump has repeatedly questioned the validity of Obama's birth certificate, and Romney's camp has done nothing to shut down his chatter.

The ad pushed supporters toward a URL, FiretheDonald.org, and asked them to sign a petition asking Romney to fire Trump from the campaign. About 2,000 have signed the petition, American Bridge said in its email today.

“It’s up to real Americans like us to show Mitt there’s a price to pay for this kind of gutter politics," the email read. "And we have to hit him where it counts -- right in the checkbook.”