WASHINGTON - The Democratic left still smarts over President Obama's failure to deliver on some of its key issues, but has made no serious move to challenge him in 2012. Even the loudest critics among them think putting up a primary candidate would just split the party and strengthen the Republican who runs against him or her. "There is beginning to be some chatter about running a candidate from the left, but nobody wants to think that way," said Peter Daou, a liberal blogger and ex-digital media adviser to Hillary Clinton's campaign. The left's grievance list is long. They believe...