Todd S. Purdum highlights the benefits of changing one's stance:
For F.D.R., who blithely explained his abandonment of domestic priorities after Pearl Harbor by saying that "Dr. New Deal" had become "Dr. Win the War." For Harry Truman, who overcame his border-state background to de-segregate the military, and for Lyndon Johnson, who abandoned his career-long opposition to strong civil-rights measures to pass the strongest ones in history as president. Here’s to Nixon in China, Bill Clinton on a balanced budget, Barack Obama on closing Guantánamo. Oh, wait! So it’s not a perfect theory.
But we’d all do well to remember the first political statement Abraham Lincoln ever made, on March 9, 1832, in his failed campaign for the Illinois legislature. … "Holding it a sound maxim that it is better to be only sometimes right than at all times wrong, so soon as I discover my opinions to be erroneous, I shall be ready to renounce them."
The Dish 