Northwestern law professors Stephen Calabresi and John McGinnis make the case for McCain in today'sWSJ. Focusing specifically on judicial nominations, they argue that electability should be a conservative's paramount concern.

the gulf between Democratic and Republican approaches to constitutional law and the role of the federal courts is greater than at any time since the New Deal. With a Democratic Senate, Democratic presidents would be able to confirm adherents of the theory of the "Living Constitution" -- in essence empowering judges to update the Constitution to advance their own conception of a better world. This would threaten the jurisprudential gains of the past three decades, and provide new impetus to judicial activism of a kind not seen since the 1960s.

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.

The judiciary is different. On Jan. 20, 2009, six of the nine Supreme Court justices will be over 70. Most of them could be replaced by the next president, particularly if he or she is re-elected. Given the prospect of accelerating gains in modern medical technology, some of the new justices may serve for half a century. Even if a more perfect candidate were somehow elected in 2012, he would not be able to undo the damage, especially to the Supreme Court.

Calabresi and McGinnis suggest nominating Romney would risk a "Goldwater-like" electoral catastrophe, and that conservatives opposed to McCain are making the perfect the enemy of the "very good."