Rand could use the high profile platform of the debate to transition to a triangulated approach, by clarifying where he agrees with Trump on a key issue, and then distancing himself from both Trump's blustering, policy-free approach and the establishment's extreme put downs of Trump. Rand needs to position himself as also bring anti-establishment, but with substance and principle.
Post-debate, he could then continue to transition, by answering every question about Trump with "I understand what he's basically concerned about, but the media's been out to lunch attacking him on it," and then present his statesman like version of the anti-establishment position. This way, he will be stealing Trump's themes, instead of appearing to attack his supporters.