It's hard to win a Senate race if you've never won an election before

The reason that experience in winning past elections can send a valuable statistical signal isn’t necessarily that experience in elected office is valuable unto itself. (For instance, candidates who are appointed to the U.S. Senate following a vacancy have poor track records at winning a Senate term for themselves). Rather, it’s the act of winning an election that counts, since it’s a sign that a candidate is acceptable to some reasonably large group of voters…

Democrats have an average experience score of 2.5 in these races, and all the candidates they’ve nominated or are projected to nominate qualify in at least the second tier of experience. Republicans’ average experience rating is just 1.0, by contrast. That’s partly because they have fewer incumbents running, but even if you exclude incumbents from the average, there’s still a huge gap: non-incumbent Democrats have an average experience rating of 2.0 versus 0.5 for Republicans.

Indeed, the Republican nominees for Senate in Arizona, Colorado, Georgia, Ohio and Pennsylvania have never held elected office before. Nor has the party’s presumed nominee in New Hampshire, Donald Bolduc.4