To get a sense of what kind of candidate each party was nominating, FiveThirtyEight collected endorsement data during primary season for all Democrats and Republicans running in races where their party wasn’t fielding an incumbent. By tracking the candidates who won early primary endorsements from various ideological groups, we can get a better sense of the future of intra-party dynamics in the 116th Congress.
For instance, Trump endorsed 11 Republicans running for open or Democrat-held House and Senate seats during the primary season. And although Trump has endorsed many more candidates since, we will be monitoring races involving those who received an early bump from the president. We’ll also be tracking the success or failure of candidates backed by conservative groups like the National Rifle Association, Tea Party Express and Club for Growth. For Democrats, we’ll monitor candidates endorsed by groups like Emily’s List and VoteVets, as well as Our Revolution and Indivisible, which support more progressive Democrats.