I think he is brining some issues to light among GOP voters (campaign finance, trade, foreign policy/Israel, health care, taxes on hedge funds) that have not been heard en masse since Pat Buchanan sought the nomination (although, Rick Santorum opposed free trade deals during his 2012 run). I vote that Trump should stay in the GOP, whether he tarnishes the Party's brand or not, and help to move the Party back to the center-right, as opposed to the far-right.
Trump is trying to move us to the center-left. Cruz and his allies are the center-right the establishment is the center. You dems need to understand that we (America) are a center-right nation and have been since JFK.