The morning after President Barack Obama’s campaign said it would start supporting Priorities USA, a Super PAC fundraising group designed to keep him in office, Republican Mitt Romney’s campaign announced it had been endorsed by James Bopp, a lawyer who advised Citizens United in the Supreme Court case responsible for the creation of the outside fundraising groups.

“Mitt Romney is a true conservative,” Bopp wrote in an “open letter” explaining the endorsement. “One does not have to guess what Mitt Romney would do in office. He served for four years as Governor of Massachusetts and has a record that conservatives should be proud of.”

Obama opposed the Supreme Court’s 2010 ruling in a case that erased limits on corporate and union money in federal elections. His campaign said he had made the switch because Republicans had raised and spent so much Super PAC money.

“With so much at stake, we can’t allow for two sets of rules,” campaign manager Jim Messina said in an email to Obama supporters.

Restore Our Future, a Super PAC supporting former Massachusetts Governor Mitt Romney, the front-runner in the race for the Republican nomination to oppose Obama’s re-election bid, raised $30.2 million in 2011 and had cash on hand of $23.6 million at the end of the year. Priorities USA, by contrast, had raised $4.2 million by the end of 2011 and had $1.5 million in cash on hand.