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In early 2007, with violence in Iraq spiraling out of control, President Bush announced a surge of nearly 30,000 U.S. troops into the country. By year's end, the violence had declined markedly and Iraq had been put on a path toward stability.

Fast-forward two years, and President Obama decided on a troop surge for Afghanistan of like proportions. The top U.S. general in Afghanistan, Gen. Stanley A. McChrystal, had asked for up to 40,000 troops to supplement the 68,000 U.S. troops already there.

Another 35,000 troops have been provided by America's International Security Assistance Force (ISAF) coalition partners. As Mr. Obama weighed Gen. McChrystal's troop request, leaked to the public in September, some Republicans accused the administration of dithering. Administration...