The farce of foreigners suing Americans for defamation in overseas forums, where the law does not sufficiently protect free speech, is so well-known that it has a fitting nickname: libel tourism. And London is its hot destination. Particularly since 9/11, foreign nationals have cynically exploited British courts in an attempt to stifle any discussion by American journalists about the dangers of jihadist ideology and terrorist supporters.

At long last, U.S. politicians are waking up to the dangers posed by libel tourism, which...