Six of the nine Missouri state senators running for re-election—all Republicans—face contested primaries. That equals 67% of incumbents seeking re-election, the highest rate since 2014. This is also the first cycle since 2014 with more than one Republican incumbent facing primary challengers.
A primary is contested when there are more candidates running than available nominations, meaning at least one candidate must lose. Historically, however, Missouri incumbents tend to win contested primaries.
