If President Obama wins reelection by three or four Electoral College votes next month, the reason may be simple: noncitizens, mostly immigrants, who don’t have the right to vote. No, I’m not talking about his immigration policy or his popularity with Latinos. Nor does this have anything to do with voter fraud. Rather, an Obama victory could hinge on a quirk in the Constitution that gives noncitizens, a group that includes illegal immigrants and legal permanent residents, a say in electing the president of the United States. As required by Article I and the Fourteenth Amendment, the decennial census, which...