According to post-debate polls Romney handily defeated Obama tonight. A response I'm seeing from the Left (e.g. here) is, "So what? Mondale and Kerry (and/or Dukakis and/or Perot) won their respective opening debates." But they weren't Republicans. Has the GOP nominee ever won the first debate decisively and gone on to lose the election? Maybe Jay Cost knows.
(Added 11/7/12) Well, now it's happened at least once.