In further evidence that the Democratic primary is straining the party, liberal activist organization MoveOn.org is circulating a petition that attacks a group of Sen. Hillary Rodham Clinton’s (D-N.Y.) donors, who had “threatened” House Speaker Nancy Pelosi (D-Calif.) for her stance on superdelegates. “This is pretty outrageous: a group of Clinton-supporting big Democratic donors are threatening to stop supporting Democrats in Congress because Nancy Pelosi said that the people, not the superdelegates, should decide the presidential nomination,” said MoveOn, which is backing Sen. Barack Obama (D-Ill.), in an e-mail to supporters. A group of deep-pocketed donors had, in a letter...