Only one of the In or Probably In candidates holds public office, and that is Ron Paul who in the House of Representatives is often on the minority side of 422-1 roll calls. All five of the out candidates holds public office, though Barbour will leave the governorship at the beginning of 2012 and Daniels will do so at the beginning of 2013. The demands of running for president and of tending to official duties have some impact here.The observation is probably correct, although Michele Bachmann is probably a candidate, and I suppose she has a better chance of winning than Paul. However, unless Rick Perry jumps in and wins, which seems in combination fairly unlikely, or the far less likely event of some other currently elected pol jumping in and winning, it sure looks like the GOP will nominate an unemployed politician this time around.
But as I said before, this isn't a normal consequence of "the demands of running for president," because Romney or Pawlenty or whoever is going to be the first unemployed nominee since Walter Mondale in 1984. Since then, all twelve nominees (including a few sitting presidents) were all currently serving in office when nominated. Barone may be thinking about the first few cycles after reform, when it became conventional wisdom that being unemployed was an advantage after Jimmy Carter, Ronald Reagan, and Mondale all won. But that didn't pan out over time. At least not until this cycle, when the Republicans will most likely break the streak.