Katherine Bagley: Wisconsin Governor Scott Walker joined the crowded field of Republican contenders vying for the White House in 2016 on Monday, and immediately stands out for having one of the poorest records on environmental and climate issues, according to green groups and political experts. Since taking office in 2010, Walker has dismantled several longstanding policies protecting wetlands and waterways, fast-tracked mining projects, fought climate action, slashed funding for dozens of state scientists and environmental...