What happens if a state has to elect both of its US senators in a single election? How is it determined which seat each person is running for? Like you have two GOP candidates and two Dems, so how do you know which R is running against which D, and how is that decided, and how do the primaries work? It all seems like it would be very confusing. And then once they end up on that cycle, the state could be going through that every 6 years for quite some time.
It would never happen that way.
Article I, Section 3 of the Constitution states that after being sworn in the first time, the Senate would be divided into three classes. Each of those classes is up every six years, with class A being elected this year for instance, B in 2004, and C in 2006, and A again in 2008.
Should there be a vacancy, a special election is held (as in Tennessee in 1994, when Fred Thompson was elected to fill Al Gore’s seat (which was being filled by Harlan Matthews) and Bill Frist also won his seat that year (vs. Sasser)). Thompson then had to run for re-election in 1996, which which was the original end of Al Gore’s term. Frist ran for re-election in 2000.
and I am sure it is just like any other election… you look at the ballot and it says John Doe ® and Jim Smith (D) on one section and Bob Davis ® and Bill Jones (D) on another…
but those are pretty rare… most of the time there is only one senatorial election going on at the same time…
check out this site for more information about elections http://bensguide.gpo.gov/9-12/election/senators.html
Thanks for the answer. I didn’t realize that special elections didn’t always give a 6 year term, I figured the alternating cycles would get screwed up eventually. Appreciate your help 
I see how they split 'em up at the start…but wouldn’t a new state when it enters the Union have two senators on the same cycle? I guess they just arbitrarily choose one term to be longer than the other? And with no incumbents, and two seats open, I bet that’s a wild election.
Happened in CA in 1992 - both Senate seats were open at once, when Pete Wilson resigned a senate seat to become governor. Boxer got a full 6 year term, Feinstein’s initial term was only for 2 years, the remainder of Wilson’s term. Neither election had an incumbent - Alan Cranston had just retired from the other seat at the end of his term.
When they brought in Alaska, both senators got short terms - 2 years and 4 years, which were voted on simply as the “A” and “B” term:
http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=150637
Whoops, the link I meant was:
Just to emphasize, the California and Alaska situations described by yabob work differently. When an existing state holds two elections at once, candidates know in advance whether they’re running for the short term or the full term. When a new state holds two elections, you run either for Seat A or Seat B, and the determination as to which seat gets assigned to which “class” (that is, which of the three staggered election cycles) isn’t made until the winners are sworn into the Senate.
In either case, however, the candidates choose which seat to run for at the time that they file their nominating petitions to get on the primary ballot, so per the OP, there is no confusion about who is running against whom.