Could be it was because he was from Western Wisconsin, could be because he didn't do anything: "A Fiscal Conservative, Van Hollen Under Spent His Budget During All Three Of His Years As U.S. Attorney." (Current scrawl on his campaign website.)
What does being a fiscal conservative have anything to do with prosecuting crime? "Gee, I'd like to send that cocaine cartel leader to prison, but I promised I'd underspend my budget by 10%. Guess I gotta let him go." Give me a break. Hire the extra staffer your budget allows and prosecute another bad guy. You know, like maybe a public official misusing a state vehicle and then lying about it after a drunk driving arrest. Get some headlines, go for it!