You can run in this circle as long as you want. If the FDA execs and the McKinsey execs reach a mutual understanding of the circumstances, including the fact th

You can run in this circle as long as you want. If the FDA execs and the McKinsey execs reach a mutual understanding of the circumstances, including the fact that McKinsey is going to be simultaneously serving unnamed third parties with contrary interests, and that this is ok, then the reasonably prudent person will conclude that these are not factors to cause them to question the contractor's impartiality. It would not be surprising to me at all if additional language in the contract explicitly address this point.