So, why have he and his mother, former first lady Nancy Reagan, made stem cell research their cause celebre?

"For people to suggest that [Nancy Reagan] shouldn’t support this because it isn't Alzheimer's ... that’s very small," a defensive-sounding Reagan responded.

He says he still backs the campaign for embryonic stem cell research because it might cure other diseases such as Parkinson's and diabetes.

But Reagan became the nation's foremost spokesman for stem cell research largely based on the notion that it might have saved the beloved 40th president, something he now acknowledges isn't true.

The revelation could prove particularly embarrassing for the national press, which has printed hundreds of stories in recent days touting stem cell science as a cure for Alzheimer's.

Tuesday morning's New York Times report was typical:

"Scientists theorize that the cells, which give rise to all other cells and tissues in the body, could yield treatments for Parkinson's disease, diabetes and, perhaps, Alzheimer's disease, which former President Reagan had."

Monday night NBC's Kelly O'Donnell noted that "John Kerry believes the work could lead to new cures for diseases like Alzheimer's."

But now that Reagan has contradicted the top Democrat, it's not clear whether Sen. Kerry will publicly acknowledge that he and Reagan are at odds over the potential for stem cell research as a cure for Alzheimer's when Reagan addresses the Democratic convention at the end of this month.

Editor's note: