I think I can call this one a Catch, even though Jamelle Bouie doesn't respond to a specific proponent of the idea that Mitch Daniels might be the moderate GOP candidate for president. Bouie points out, quite correctly, that if Daniels does run, he'll adopt the positions that the bulk of the GOP holds. In other words, he'll either run as a conventional conservative Republican, or he won't stand a chance.
This reminds me to tweak Nate Silver's graph of Republican candidates and potential candidates a bit. On two counts. One is that it's difficult to predict where candidates will position themselves before they run; yes, they're constrained to some extent by their past, but generally it's a safe bet that moderates entering their party's presidential nomination contest will shift to positions on public policy issues that match consensus positions taken by important party groups and constituencies. In other words, GOP moderates will move right to win the nomination.
The other, and it's a quibble, is that it's a bit misleading to divide space, as Silver does, into equal parts. There's no reason to assume that there is as much political space on the "moderate" side as on the "conservative" side. Even if you carefully draw the midpoint to force two equal parts, the "space" might well correspond to the simple model Silver's graph implies. In other words, his model implies that Mitt Romney has an advantage because he occupies a less crowded part of GOP political space, but in order to conclude that we'd need to know a lot more about the distribution of views among the Republican organized groups and constituencies who matter in presidential nomination politics.