This section is from the book "The Constitutional Law Of The United States", by Westel Woodbury Willoughby. Also available from Amazon: Constitutional Law.
The Constitution provides that for the election of Representatives to Congress, "the electors in each State shall have the qualifications requisite for electors of the most numerous branch of the state legislature." This places the determination of who may exercise the suffrage wholly within the control of the States, except for the restriction placed upon them by the Fifteenth Amendment. There thus exists the rather curious fact that the National Government though able to control its citizenship by naturalization is not able to confer the suffrage for the election even of its own officials; whereas the States may confer, and, indeed, in a number of instances have conferred this suffrage upon persons not citizens of the United States.7