America can still avoid sharing Europe’s fate. But only if we take action. Because of what Europe has become, it now has few viable choices in dealing with radical Islamic terrorism. Its dilemma is a warning to Americans that we should turn away from a similar path of national suicide. After suffering serial terrorist attacks from foreign nationals and immigrants, a normal nation-state would be expected to make extraordinary efforts to close its borders and redefine its foreign policy in order to protect its national interests. But a France or a Belgium is not quite a sovereign nation any more,...