World leaders arriving in Washington for President Obama's Nuclear Security Summit must have felt for a moment that they had instead been transported to Soviet-era Moscow. They entered a capital that had become a military encampment, with camo-wearing military police in Humvees and enough Army vehicles to make it look like a May Day parade on New York Avenue, where a bicyclist was killed Monday by a National Guard truck. In the middle of it all was Obama -- occupant of an office once informally known as "leader of the free world" -- putting on a clinic for some of...