The $2.5 billion earmark/loan that John Thune sought for the Dakota, Minnesota & Eastern Railroad last year should disqualify him from getting any real conservative support for this slot.
This debacle tarnished his status as a rising star in the conservative movement.
Luckily, the Federal Railroad Administration denied it in the end, but Thune never appeared to learn his lesson.
Update: Gosh, we have good commenters. Thune also voted for the bailout. That should be another disqualifier.