Every year, the Senate Select Committee on Intelligence is briefed by the chief of U.S. intelligence on potential threats to the nation. The list is sobering, but usually predictable and typically includes global terrorism, nuclear proliferation and regional conflicts.

But this year, there was a surprising potential foe: the falling dollar. In his report to Congress last week, Director of National Intelligence Michael McConnell went beyond the conventional world of spycraft. Mr. McConnell specifically acknowledged "concerns...