He must be seen as a threat. They've already probed his college career more than they did Obama's. Despite the headline, as the story goes to show, there really is no mystery as to why Walker left college: he found a good job.
http://www.washingtonpost.com/politics/as-scott-walker-mulls-white-house-bid-questions-linger-over-college-exit/2015/02/11/8e17ea44-b13e-11e4-886b-c22184f27c35_story.html
http://www.washingtonpost.com/politics/as-scott-walker-mulls-white-house-bid-questions-linger-over-college-exit/2015/02/11/8e17ea44-b13e-11e4-886b-c22184f27c35_story.html