The Chinese government hacked into U.S. defense systems. What makes Americans think that the Chinese—or the Russians, the Iranians or other foreign interests—are not also hacking into U.S. elections? They may well be doing it on a large scale. But Americans have no way to know. We have certainly made it easy for them, especially after the U.S. Supreme Court’s Citizens United ruling, handed down five years ago. U.S. law prohibits foreign nationals from making a contribution or donation in connection with any federal, state or local election. The prohibition includes contributions to candidates and political action committees, as well...