The obvious answer is Dem hackery.
But there's also the fact that most of the time a Senate challenger is going to have far higher name recognition than a House challenger does because the races are much higher profile.
If it is just an issue of name recognition, then isn't it even worse for a Senate incumbent to be below 50? That would suggest that a House incumbent that is below 50 may be able to pick up some support simply by running some ads and increasing name recognition.
I think the point was that the
challenger tends to have much lower name recognition in House races than Senate races, and thus more room to grow.
But I don't really think the 50% threshold is particularly magical in either case. The margin is much, much more important.
