Progressives are taking shots at Joe Biden, seeking to blunt the former vice president’s rise in polls by arguing he is too conservative to be the party's presidential nominee. The criticism has come from rivals to Biden on the campaign trail as well as liberal groups seeking to put a dent into his poll numbers. They are casting Biden as an establishment figure out of touch with the grass roots of his party, highlighting his work on a Clinton-era crime bill and the Iraq War, among other issues. The criticism suggests some angst on the part of progressives, who fear...