Zogby, the polling firm that usually brings good news for the left, has some bad news for Barack Obama: He’s down amongst his key demographics, including African Americans, young voters, and Catholics.

Barack Obama has lost ground among some of his strongest bases of support, including young people, women, Democrats and independents, according to a new ATV/Zogby poll.

The Illinois Democrat has also lost some support among African-Americans and Hispanics, where his lead over Republican John McCain has shrunk, and among Catholics, where he’s lost his lead.

He’s lost 36 points in the 18-29 demographic, now leading McCain just 11. He used to lead amongst Cathlics by 11, but now trails by 15.

So what did it? Zogby says the World Tour was responsible.

He attributed Obama’s erosion of support to McCain’s criticisms of Obama as inexperienced in the wake of Obama’s trip to Europe, the Middle East, Afghanistan and Iraq and to Obama’s flips on some issues.

“The survey results come as Obama, fresh off what had been characterized as a triumphant tour of the Middle East and Europe, including a speech to 200,000 Germans in Berlin. That trip quickly became fodder for an aggressive response ad by the McCain campaign that questioned whether Obama’s popularity around the world meant he was ready to lead the U.S.,” Zogby said.

You know, the same ads everyone made fun of as ineffective.