Lexington on populism

In The Economist, the Lexington columnist this week writes on populism, arguing it will remain a factor in American politics even if the main populists in the presidential campaign have lost, a fact that seems not to matter to Lexington, presumably a committed populist. The arguments that John Edwards, the most committed populist of the presidential candidates, made were contrived and unconvincing. The majority of registered Democrats, the most liberal of Americans, weren't buying what Edwards was selling. Why would America's remaining political candidates choose to run for office using populist arguments that the majority of voters have already rejected?