Warning about "weapons designed for the theater of war," President Obama on Wednesday called for immediate action on a new Federal Assault Weapons Ban. He said that "more of our fellow Americans might still be alive" if the original assault weapons ban, passed in 1994, had not expired in 2004. Last month, in the wake of the horrific shooting at Sandy Hook Elementary in Newtown, Conn., Sen. Dianne Feinstein (D., Calif.) promised to introduce an updated version of the ban. She too warned of the threat posed by "military weapons."

After...