WASHINGTON -- Most media polls are showing President Obama's job approval in the 59 percent to mid-60 percent range, but not pollster John Zogby, who says Obama's rating has dipped below 50 percent.

Contrary to many of the other major presidential surveys such as the venerable Gallup Poll, which puts Obama's number at around 60 percent or higher, Zogby's poll (mid-March) showed that Obama's job performance fell. His findings are significant for a number of definitional reasons and are worth a closer look.

In his most recent survey, the pollster said that "49 percent rate his job performance as excellent or good, and 50 percent as fair or poor (less than 1 percent were not sure). That is a dip of 3 points from the previous poll," Zogby said last week.

His numbers, as with other pollsters, show a huge partisan divide in how Americans rate Obama at this point in his young presidency. Ninety-one percent of Democrats score Obama favorably, compared with only 14 percent Republicans.

On job performance alone, 87 percent of Democrats rate him excellent or good, compared with just 9 percent of Republicans.

But if Gallup scores Obama's job performance at 60 percent or better, why are Zogby's numbers so much lower?

Zogby told me that he uses a scale that ranges from excellent to good on the positive side versus fair to poor on the negative. "If you look at the fair rating for Obama, that was 12 percent. If you split that, because some people think fair is approve, then you're up in the mid-50s," he said.

In Zogby's differential rating scale, "fair is a negative because it doesn't get you anywhere. Presidents don't run on the basis of saying reelect me, I did a fair job," he told me.

Other polls put their fair responses into their favorable percentage, and thus produce a larger approval number for the president in their surveys.

Obama's numbers have declined for several reasons, according to Zogby. For one thing, "expectations are very high," he said.

That's largely Obama's doing. He raised them by saying he could and would wipe away every problem the country faced: Fixing the economy, raising spending for a huge range of social-welfare problems, cutting middle-class taxes, enacting national healthcare, and developing alternative-energy sources to end our dependence on foreign oil.

It didn't take long for many Americans to realize that he could not do all of these things at once, and may not be able to some of them at all. Continued...