In the rush to assign blame for the Christmas shopping frenzy that is taking hold earlier than ever - detractors assailed Target, Toys R Us, and Walmart for planned Thanksgiving openings this year - one must follow the fingertips of American shoppers.

Because the bogeyman boils down to this: online, online, online.

For decades, retailers made a bundle on Black Friday by packing stores with sale goods, filling Thanksgiving Day newspapers with advertisements, and reveling in revenue as customers rolled in the next day en masse.

Then came the Internet. And the old model crumbled like a Jenga tower at a holiday party. Retailers that open their doors at ungodly hours on and after Thanksgiving are competing with an online shopping realm where the doors never close.

Tons of people trawl the Internet on Thanksgiving as the turkey roasts and the relatives squabble over old beefs. Still others click-and-buy on the days before and after, and all through Christmas, depending on which discounts land in their e-mail.

Rather than let that business vanish forever, brick-and-mortar retailers opt to open earlier - an enticement aimed at damage control.

"Will people wait in line in these harrowing situations, or will they just stay in their living room and purchase if they can get the same kind of deals?" asked Wharton School marketing professor Barbara Kahn, articulating the quandary in which store-based retailers find themselves.

"If people buy somewhere else, they're less likely to shop with you," added Kahn, director of the Jay Baker Retailing Center at Wharton.

That's exactly the foe retailers are fighting.

Purchases that used to be made exclusively at a cash register in a department store, toy store, or electronics retailer are increasingly taking place on a Web page.

Also, big sales on the Web do not occur just one or two days around Black Friday - they're spread out, making for an even stealthier moving competitive target.

"We expect online spending to increase about 15 percent year over year, far outpacing the growth in overall holiday sales," Margaret Taylor, vice president and senior credit officer at Moody's Investors Service, said in a report Tuesday. "Consumers continue to be enticed by the ease of online shopping, as well as the ability to find good deals online."

Web shopping will draw so much more interest this year, Moody's said, that it will be the bright spot against an overall holiday-sales growth projection of 4 percent, compared with 6.5 percent in 2011.

Making matters even trickier is the way online retailers spread sales over many days, to keep high volume from overloading their sites, Kahn said.

Last year, the single biggest day for U.S. retail spending online was Thursday, Dec. 1 - a full week after Thanksgiving, according to estimates tabulated by MasterCard Advisors SpendingPulse, spokesman Meir Kahtan said.

As though all this were not sobering enough for companies that stock, heat, staff, and keep stores open through the holidays, there is yet another enemy:

The very retailers being criticized on moral grounds for opening on once-untouchable days are in this predicament in part because they are being exploited by increasingly wily shoppers.

"Showrooming," as it is known in the industry, is when a customer strolls into a store, inspects a popular product, then compares its price on a smartphone or leaves to order it online. (One edge that online retailers have on price stems from the fact that they do not carry the overhead associated with actual stores.)

"One of the biggest competitors to Walmart right now is Amazon," Kahn said. "These online competitors, there's no question, are changing the way brick-and-mortar retailers do business."

Even with the threat of Black Friday protests, planned at Walmart stores in Philadelphia and across the country, and other campaigns against store-based retail corporations this year, there is no doubt consumers are also behind the market shift.

Deloitte L.L.P., in its own annual holiday survey a few weeks ago, found that 27 percent of respondents would do the majority of their shopping online, while 45 percent would shop online during the holidays.

Even Consumer Reports said Wednesday it found in a poll that two-thirds of Americans (68 percent) would not be shopping at stores on Black Friday.

And Cyber Monday, the online world's response to Black Friday, appears to be building a following, according to online shopping site

That firm's survey found 41 percent of people would shop on the Monday after Thanksgiving, up from 37 percent last year and 33 percent in 2010.