The problem is his record and personal history. He lied about his military service. He had a drunk driving incident: he drove 96 in a 55 mile per hour area.

Edit:

https://nypost.com/2024/08/06/us-news/tim-walz-past-dui-arrest-for-driving-96-mph-in-a-55-zone-comes-back-to-haunt-vp-pick/