What are you talking about?  The Senate race, in 2018, has 23 Democratic and 8 Republican seats up for grab. Of those 31 seats, it is projected, by most political analyst, that the Republicans will gain between 8 and 11 Democratic seats. The notion that the Republicans will walk away from the elections next year, with anything less than a super-majority in the Senate, is highly unlikely - irrespective of how the Senate race goes in Missouri.