Stephen Calabresi and John McGinnis have this op-ed in the WSJ. Here is a snippet:
We believe that the nomination of John McCain is the best option to preserve the ongoing restoration of constitutional government. He is by far the most electable Republican candidate remaining in the race, and based on his record is as likely to appoint judges committed to constitutionalism as Mitt Romney, a candidate for whom we also have great respect.
We make no apology for suggesting that electability must be a prime consideration. The expected value of any presidential candidate for the future of the American judiciary must be discounted by the probability that the candidate will not prevail in the election. For other kinds of issues, it may be argued that it is better to lose with the perfect candidate than to win with an imperfect one. The party lives to fight another day and can reverse the bad policies of an intervening presidency.