Trump and the Koch network are the GOP's most effective endorsers by far

Measuring the effect of a political endorsement is tricky: For some voters, it may be a determining factor. For others, it may simply match previously-held beliefs. But endorsements do offer a telling gauge of how a political party's base is thinking. For the Republican Party in 2018, endorsements from President Trump and the Koch network correlate with victory by a large margin. Nearly 90 percent of the candidates who gained these coveted affirmations won their primary this year, a FiveThirtyEi...