Two hundred and fifty years after the Declaration of Independence, we speak of the founders with a reverence that can flatten them into marble—preordained, wise, and magnificent. But George Washington is a far more interesting figure than the monument allows. He was, by most accounts, a mediocre battlefield general. He lost more engagements than he won. He was outmaneuvered at Long Island and badly beaten at Brandywine, and lost Philadelphia in the aftermath. As president, of course, he was transformative, setting precedents for executive restraint and the peaceful transfer of power that still define the office.But neither the flawed general...