WASHINGTON — Paul D. Ryan and his self-proclaimed "young guns" in the House Republican leadership traversed the country in 2010 harnessing the energy of the Tea Party movement that would sweep them to power that November. But in failing to confront the most divisive forces of the movement, they may have set their party up for its current crisis. Some of those insurgent winners from that year would eventually turn on the leaders one by one, setting in motion the downfall of Representative Eric Cantor -- just as Republicans were attempting to cobble together a modest immigration measure -- then...