Mark Steyn makes the argument for warrantless wiretapping when one-half of the call is outside of the US as well as can be done in two sentences…

If Judge Taylor’s ruling stands, if the U.S. government intercepts a call from Islamabad to London about a plot to blow up Big Ben, it can alert the Brits. But, if the U.S. government intercepts a call from Islamabad to New York about a plot to blow up the Chrysler Building, that’s entirely unconstitutional and all record of it should be erased.