It’s technology that also allows an unprecedented level of precision. During the 2009 New Jersey governor’s race, Chris Christie launched an Internet-based defense of a tough attack from then-Gov. Jon Corzine. The Democrat had accused Christie of supporting policies that would cut funding for medical screening services, such as mammograms.

CampaignGrid, the online advertising firm that worked for Christie in that race, targeted a precise segment of female voters in the Garden State with an online response ad. “Mammograms save lives,” the ad read. “Chris Christie knows firsthand—a mammogram saved his mom. Watch now.”

Rockefeller’s bill would drastically change this new environment. If large swaths of voters began to opt-out, the effectiveness of efforts like the one Christie’s campaign employed would undoubtedly be stunted.

Political consultants were warned of a similar doomsday scenario when Do Not Call registries were established in 2003. In the end, politicians were exempted from the list, prevailing on a freedom of speech argument. Some privacy advocates, including Lillie Coney with the Electronic Privacy Information Center, fully expect campaigns to get that same protection this time around should Do Not Track legislation actually make it through Congress.

“It’s one of the last things added, typically,” Coney says of language that would exempt campaigns from any Do Not Track standard. “I would be very surprised if anything makes it through the process without that language.”

Others aren’t so sure. An exemption for politicians this time around could be a stretch, some argue, because Do Not Track legislation isn’t necessarily about stopping a form of speech.

“Tracking is different—you either can track or you can’t,” says Latterman. “With political stuff you do start to move into free speech. But tracking isn’t speech; it’s collecting data.”

The relative success of Do Not Call legislation seems to be coloring the congressional debate around Internet tracking policy. Many consumers were relieved when they were empowered to block telephone marketers, but the Do Not Track list probably would have the opposite effect, according to Tom Leonard, president of the Technology Policy Institute. He says an intrusive phone call at dinner time is worlds apart from an ad that pops up as you browse the Internet.

“Rather than reducing unwanted marketing messages it would likely increase unwanted marketing messages, because you would get messages that were less well targeted to your interests,” says Leonard, who has testified against Rockefeller’s bill in the Senate.

“Advertisers would have to send out a lot more messages than if the messages were well targeted.”

That’s an argument echoed by Sen. Claire McCaskill (D-Mo.), who has turned out to be a key Senate ally for marketers given her take on many of the proposed Do Not Track policies. The Democrat contends that consumers are ultimately the biggest beneficiaries of anonymized tracking.

“I just think people need to understand there are serious consequences to saying that we can’t do behavioral marketing on the Internet,” McCaskill tells C&E. “It’s going to cost consumers a lot more money to get what they’ve been getting for free if we’re not careful. So I want to make sure it’s thoroughly vetted.”

As for how the legislation could impact the political consulting community? That’s not quite the motivating force for McCaskill.

“Well, that’s the least of my concerns about the political campaigns,” McCaskill says. “My concern is that the Internet has worked so well and it is free to consumers, to the American people. The reason it’s been free is because behavioral marketing has funded the Internet.”

It’s unclear how many would opt-out if some form of Do Not Track were to become law, but an array of surveys show a growing level of concern as people are slowly learning their online movements are being documented and then sold to advertisers and eventually politicians. A recent online Wall Street Journal survey that accompanied a series of articles on how marketers track consumer behavior, found that 59 percent of respondents were “very alarmed” by how companies track the online footprints of users.

“This is an area where I think we need some clarification,” says Arkansas Democratic Sen. Mark Pryor, a cosponsor of Rockefeller’s legislation. “I think the consumer, you know the John Q. Citizen, should have the right to know if he’s being tracked. Right now, I think a lot of people would be surprised to realize how often they are being tracked and they have no idea.”

Even if lawmakers muster the votes, implementing a new regulatory system could prove even tougher than getting a bill through Congress. Whatever emerges, consultants are hoping for a slow, methodical approach.

“If the timeframe is aggressive for good actors in the marketplace to get aligned with that new legislation, I think it could have a more material impact for the industry,” says Andy Hunn, the chief operating officer at Resonate Networks. “One of the big questions still unanswered is to what degree are preexisting approaches to trying to protect online privacy, like the self-regulatory efforts of the online ad industry, going to be grandfathered in under the new legislation?”

Putting the current legislative bottlenecks aside for a moment, the fate of Do Not Track is just as uncertain given the dozens of new lawmakers who have yet to form opinions on a topic that doesn’t lend itself to an easy ideological calculation.

“On the one hand, we don’t want to discourage innovation and discourage providers from going into unique lines of business that have made our lives easier,” says Florida freshman Sen. Marco Rubio (R). “On the other, I’m not sure that all of our private information like that should be available to people to use for consumer purposes. So it’s an interesting issue from an intellectual perspective and I’m still forming an opinion on it based on information I’m getting.”

Matt Laslo is a Washington D.C.-based freelance journalist who covers Congress and the White House.

Shane D’Aprile contributed reporting.