BYRON YORK: Progressives split over Arizona convention. “The division inside the progressive world could have serious consequences. Netroots Nation attracts the leading lights in the Democratic Party — this year’s meeting in Detroit featured Vice President Joe Biden and Sen. Elizabeth Warren. In 2015 the party’s presidential race will be fully under way. With some key elements boycotting the Phoenix convention, will top Democrats attend or stay away? Their decisions could lead to charges that one candidate or the other, or one faction or the other, is insufficiently pure on immigration, an issue that many Democrats count as one of the party’s great strengths. The fight inside the progressive community could spill into Democratic politics at large, at just the wrong time.”