Future historians tracing the crackup of the Republican Party may well look to May 8, 2010, as an inflection point. That was the day, as is now well known, that Sen. Robert Bennett, who took the conservative position 84 percent of the time over his career, was deemed not conservative enough by fellow Utah Republicans and booted out of the primary. Less well known, but equally ominous, is what happened that same day, 2,500 miles east in Maine. There, the state Republican Party chucked its platform -- a sensible New England mix of free-market economics and conservation -- and adopted...