In the hours after Sen. John McCain announced his choice of Alaska Gov. Sarah Palin to be his running mate in the last presidential race, members of an online forum called Journolist struggled to make sense of the pick. Many of them were liberal reporters, and in some cases their comments reflected a journalist’s instinct to figure out the meaning of a story. But in many other exchanges, the Journolisters clearly had another, more partisan goal in mind: to formulate the most effective talking points in order to defeat Palin and McCain and help elect Barack Obama president. The tone...