Peterson's seat would not be hard to hold. The DFL bench is very good with lots of strong candidates in the legislature, while most of the Republicans in the legislature in the area are mostly nutters. I refer you all to here: https://uselectionatlas.org/FORUM/index.php?topic=61179.0
It's probably more likely Peterson would be replaced by a more liberal Democrat than a Republican. Herseth is a bad move though.
Didn't you also call Paulsen a nutter [qm].
Anyway, any PVI R+4 open seat is a question mark in my book.