Yeah, Johnson not running for re-election actually hurts Democrats unless the GOP runs an extremely boring candidate.
How so? If Johnson ends up not running, this is straight tossup.
Johnson is more likely to lose a general election than someone like Mike Gallagher. Of course, this will be a very hard seat for Democrats to win in the likely 2022 environment.
I know this is the conventional wisdom on the site, because Johnson is "toxic" or "extreme" or "an insurrectionist" or whatever (these are all accurate labels; the scare quotes were to imply that they don't matter electorally). But do we have any real evidence that it's true? Given his over-performance in 2016, and the innate advantages of incumbency, and his presumable popularity among Trump voters...I'm just not sure he's any weaker than Gallagher or whomever the WI GOP would put up. MT Treasurer has made some good posts on this point and could probably argue it better than me.