U.S. officials had once thought there was little chance that terrorists could get their hands on many of the portable surface-to-air missiles that can bring down a commercial jet liner. But now that calculation is out the window, with officials at a recent secret White House meeting reporting that thousands of them have gone missing in Libya. "Matching up a terrorist with a shoulder-fired missile, that's our worst nightmare," said Sen. Barbara Boxer, D.-California, a member of the Senate's Commerce, Energy and Transportation Committee. The nightmare has been made real with the discovery in Libya that an estimated 20,000 portable,...