It does seem that there should be a national database of voters, since most elections involve national elections.  But the data should be limited to the voter's name and county in which the person is registered.  Prior to any election, this list could be used to discern if any voter has multiple registrations due to having moved, and then an effort could be made by the secretary of each state to determine which registration is currently valid, thus ensuring that only-one ballot is cast.  This database could also be tied to social-security death records, to assure that dead folks don't "vote."  With computers, this would all be so simple.  I have no problem with the federal government's knowledge (or anyone else's, for that matter) that I am registered to vote in Arapahoe County, Colorado.