What are some things/elections a regular registered voter cannot partake in?
There are many elements of United States politics which are either handled through appointment or are restricted to a limited class of voters. First, voting is often geographically limited, e.g. if you are a resident of Montana, you cannot vote for the Senator for New York. Voting can also be limited in “closed” primaries to registered members of a specific political party. Some states have closed primaries in which, for example, only a registered Republican may vote for candidates to represent the Republican party in Presidential elections. When an elected official dies or resigns during her term of office, a temporary successor will often be appointed to serve out the term. Finally, many important positions in the judiciary are handled by appointment.