The real lesson heading into the 2018 midterm cycle is that Trump should be smarter about who he endorses: “On-brand” endorsements can help, but Trump doesn’t have the power, for example, to make moderate Republicans vote for an uber-conservative, or vice versa.

Endorsements, if they work at all (and often they don’t), work best when they give an ideological cue to a voter that they wouldn’t have otherwise had. That’s why endorsements rarely matter in general elections: Most voters already fit into one of the partisan camps and are going to cast a ballot based solely off party label. In a primary, on the other hand, the candidates are more ideologically similar, and so an endorsement can help voters make a choice.