Pundits who argued that GOP presidential nominee candidate Herman Cain was merely the Republican party's flavor of the month in the race to unseat Democratic incumbent Barack Obama may have been right.

While Cain is raising more money and remains firmly entrenched as a contending candidate in most polls his fleeting public star seems to be falling.

One need only to look at sales of Cain's new book, This is Herman Cain! to get an idea. In its first week of sales earlier this month, with Cain doing book tour events and signings, his memoir was among the bestsellers of new hardcover books in America, selling 12,533 units according to Nielsen Bookscan, which tracks industry numbers.

But in the second week -- albeit due in part to sold out stock among some retailers and distributors -- sales of Cain's book fell to 5,163 units, below totals needed to make most respected bestseller lists. Now, in numbers just released Wednesday by Nielsen Bookscan, which tracks some 80 percent of all U.S. book sales through stores including Barnes & Noble, Amazon and many independent booksellers, Cain's book sold just 2,504 units for the week.

On Amazon.com, the hardcover edition of This is Herman Cain! is ranked number 79 no the best sellers rank. The Kindle ebook version is ranked number 454.

The news of falling demand for Cain's book comes on the heels of a scathing article in The New York Times titled As Cain Promotes His Management Skills, Ex-Aides Tell of Campaign in Chaos. The article quotes former staffers who suggest Cain's campaign is run through disorder.

A CBS/New York Times poll released Tuesday showed Cain as the front-runner in the GOP presidential nominee race, with 25 percent of Republican primary voters pegging him as their choice, while former Massachusetts governor Mitt Romney finished second in the poll, with 21 percent.

And while Cain's fundraising is on the rise, he is also near the bottom of the ladder among the GOP candidates. The falling book sales, however, could be an early sign of Cain's popularity demise.