Through 11 presidential elections, beginning with the Democrats’ nomination of George McGovern in 1972, Republicans have enjoyed a presumption of superiority regarding national security. This year, however, events and their rhetoric are dissipating their advantage.

Hours — not months, not weeks, hours — after the last U.S. troops left Iraq, vicious political factionalism and sectarian violence intensified. Many Republicans say Barack Obama’s withdrawal — accompanied by his administration’s foolish praise of Iraq’s “stability” — has jeopardized what has been achieved there. But if it cannot survive a sunrise without fraying, how much of an achievement was it?