Sam Graham-Felsen of myBarackObama.com writes in:

For the third time in two days, Senator McCain repeated the false claim that his economic plan has been endorsed by 300 economists.

FACT: Many of the 300 economists don't support McCain's whole economic agenda. On Monday, John McCain's campaign released a statement signed by 300 economists who "enthusiastically support" his "Jobs for America" economic plan, providing a heavyweight testimonial to the presumptive Republican nominee's "broad and powerful economic agenda." There's just one problem. Upon closer inspection, it seems a good many of those economists don't actually support the whole of McCain's economic agenda. And at least one doesn't even support McCain for president. In interviews with more than a dozen of the signatories, Politico found that, far from embracing McCain's economic plan, many were unfamiliar with - or downright opposed to - key details. [Politico, 7/9/08, http://www.politico.com/news/stories/0708/11618.html]

FALSE McCAIN CLAIM: "And by the way my economic plan has been signed on to by 5 Nobel laureates and by over 300 economists, so I have my own supporters as well and again the Congressional Budget Office and others of do their calculations on static economic conditions, i don't except that." [McCain tele-town hall, 7/10/08]

FALSE McCAIN CLAIM: "Our economic plan has been supported by 300 economists and five Nobel laureates." [McCain avail, 7/9/08]

FALSE McCAIN CLAIM: "I'm saying that there is five Nobel laureates and 300 economists who think my economic plan is a good one." [CBS Evening News, 7/9/08]

When John McCain and reality square off, reality wins. Every time.