I say they can. It makes no sense, but nothing they do strategically (long-run) makes much sense to me. If Obama wins, will McConnell come out the next day and express something more like “OK, we tried to make him a one-term President, and we wrecked our brand doing nothing else–now it’s time to become the loyal opposition again” or will he doubledown on their obstructionism and vow to continue opposing anything he proposes or stands for on the principle of being able to then claim a two-term failed presidency?
This question is much bigger than McConnell himself, of course–I just use him as a handy illustration.