Bloomberg News Editor-in-Chief John Micklethwait released a memo last week saying the news agency will not “investigate” Michael Bloomberg, who has entered the 2020 race for the presidential nomination. “We will continue our tradition of not investigating Mike (and his family and foundation) and we will extend the same policy to his rivals in the Democratic primaries. We cannot treat Mike’s Democratic competitors differently from him,” Micklethwait wrote. Bloomberg News, though, will continue to investigate President Trump and Republicans. That doesn’t sit well with the Trump campaign. “The decision by Bloomberg News to formalize preferential reporting policies is troubling and...