Top Republicans in Washington and in the national GOP establishment say the 2010 campaign highlighted an urgent task that they will begin in earnest as soon as the elections are over: Stop Sarah Palin. Interviews with advisers to the main 2012 presidential contenders and with other veteran Republican operatives make clear they see themselves on a common, if uncoordinated, mission of halting the momentum and credibility Palin gained with conservative activists by plunging so aggressively into this year’s midterm campaigns. There is rising expectation among GOP elites that Palin will probably run for president in 2012 and could win the...