Presidential primary filing has now closed in fifteen states. In every Republican presidential primary so far, there are at least twelve candidates on the ballot. That is a stark difference from the past. If one looks at the previous election years in which a Republican president was not running for re-election, there were always some Republican presidential primaries with many fewer candidates. Examples: in 2012, Virginia had two; in 2008, Nebraska, New Mexico, and Oregon had two; in 2000, D.C., Indiana, New Jersey, and Oregon had two; in 1996, Arkansas, D.C., Indiana, New Jersey, and New York had three; in 1988, New Jersey had one; in 1980, Ohio had two.
Of course, in the states in which filing hasn’t yet closed, chances are there will be some states with fewer than twelve, as candidates drop out. The last state in which the list of candidates will be set (for Republicans) is South Dakota, where the date is March 29, 2016.