I understand the US constitution mandates three rolling 'classes' of nearly equal numbers of Senators be elected every two years, each for 6 year terms. The convention has been to not elect both Senators from a state in the same 'class' ie always at the same time. Could a state decide to elect them in the same class though?

As a follow up, could a state elect both Senators not just on the same ballot but in the same race. Electing the two candidates with the highest votes.

2 Answers 2


Each senator is in one of three classes, and at each election all the senators in one class are elected. In the 2018 race, for example the "class 1" senators were elected. That regular elections for different classes happen at different dates is not merely a convention, it is mandated by Article one of the Constitution.

In addition to the regular elections that choose senators for a period of six years, and are held every two years (as mandated by Article 1, as modified by Amendment 17), there are also "special elections". These occur when a senator dies, resigns or is otherwise removed from office. Special elections can be held at any time. The senator elected in a special election serves only for the remainder of the term. So if senator dies two years into their 6 year term and is replaced in a special election, the new senator may serve for the remaining four years before having to face re-electionn

It is possible for special elections for a Senate seat to be scheduled on the same day as regular elections. In which case a single ballot paper can be used for the two Senate seats (and the House seat, and any other elections occurring at the same time) This saves money and is convenient.

For example in 2018, in Minnesota, Tina Smith was elected to fill the class 2 Senate seat in a special election, while, at the same time, Amy Klobuchar was elected to the class 1 seat. Klobuchar will now serve for 6 years, while Smith will face re-election in two years time in the class two senate elections.

The constitution is allows states to organise the election as they see fit. It only requires that:

When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies.

This would seem to require that a separate election is held for the vacant seat. At any rate, there is little to gain in holding a joint election. It creates a confusing system in which the parties would game the system, entering 1 or 2 candidates according to tactics and reducing the ability of the electorate to choose their senators. No state has done this.

  • 1
    How does "for example in 2018 in Minnesota" square with "no state has done this"? Nov 13, 2018 at 11:56
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    @Henning As far as I understand, no state has done a joint election; but some (as in Minessota in 2018) have done two separate elections in the same day.
    – LordHieros
    Nov 13, 2018 at 12:21
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    Is it technically possible for states to change the classes of their senators (e.g. move both Alabama senators to class 2 and both Alaska senators to class 3)? If yes, then who has a privilege to do so? Nov 13, 2018 at 13:58
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    @defaultlocale Your question was whether states can unilaterally reassign their senators. My answer was that they can't. As for your new question, I have no idea whether the Senate can reassign classes, but I suspect not, as that would necessarily change the length of some Senators terms to something other than six, something I would suggest would be unconstitutional. Nov 13, 2018 at 17:40
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    @BrooksNelson the constitution specifies that a senator's term of office is six years, except for the first batch of senators, some of whose terms were two or four years to set up the current system. To reassign classes now, a senator's term would have to be lengthened or shortened, which would be contrary to the constitution.
    – phoog
    Nov 13, 2018 at 20:54


Article I Section 3 of the United States Constitution mandates the seats of the three class of Senators to be vacated at the expiration of the 2nd, 4th and 6th years respectively. Elections are to be held to choose one third of the Senators “every second year“.

The seats of the Senators of the first class shall be vacated at the expiration of the second year, of the second class at the expiration of the fourth year, and the third class at the expiration of the sixth year, so that one third may be chosen every second year;

So, unless there are vacancies in the Senate (see special election procedure outlined in the 17th Amendment), elections for the three different classes of Senators are mandated by the Constitution to be held every two years.

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    Does the constitution also state that the two senators of a given state need to be in different classes? If not, senators for a single state could still be elected simultaneously. Who or what determined the class, anyway?
    – Chieron
    Nov 13, 2018 at 12:17
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    @Chieron, according to the Senate's own FAQ, cited from the relevant Wikipedia article, "In the first Senate, on May 15, 1789, the total body was divided into three groups, being sure that no state had both senators in a single group, [...]", and "When new states are added, the number in each group is kept as even as possible[.]"
    – david
    Nov 13, 2018 at 15:01
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    @Chieron: Note also that if all states elected both their senators at the same time, the classes would not necessarily be divided "as equally as may be into three Classes." For example, if there were 17 states in Class 1, 17 in Class 2, and 16 in Class 3, then you'd have a 34-34-32 split, which is "less equal" than the current 34-33-33 split. Nov 13, 2018 at 17:11
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    @MichaelSeifert - When there were 49 states, we had 33, 33, and 32. Adding both from the same state to Class III would not change the current 50 state configuration of two with 33 and one with 34 that you'd get by adding one to the third class and one to one of the others. Don't know why you'd want to go that route, but "keeping it even" does not necessarily exclude the possibility of adding two from a state to a single class. Is there anything explicit that you are aware of, other than common sense, that would prevent this? Nov 13, 2018 at 20:44
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    @PoloHoleSet it could be argued that "as equally as may be" implies that no state should have two senators in the same class, and precedent certainly supports that reading. It is not, however, explicit in the constitution.
    – phoog
    Nov 13, 2018 at 21:39

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