By Paul Farhi

Will Medicare premiums go up nearly 2 1/2 times over the next two years in order to pay for the health-care legislation signed by President Obama last year? Well, no, they won't. But you might think an increase is coming if you read a chain email that has spread across the country in the past few months. "Send this to all seniors that you know," it says. "So they will know who's throwing them under the bus."

Will Americans be subjected to international gun-control laws under a new U.N. treaty signed by Hillary Rodham Clinton? Is the president honoring Jane Fonda as one of the "women of the century"? Was suspected Fort Hood shooter Maj. Nidal Hasan an adviserto the Obama administration?

Like the Medicare story, these claims are demonstrably false, too. Nevertheless, they are popular on the thriving underground email circuit, a carnival of nonsense whose star attractions have included the canard that Obama is a secret Muslim and variations on the "birther" claims about his origins.

Grass-roots whisper campaigns such as these predate the invention of the "send" button, of course. No one needed a Facebook page or an email account to spread the word about Thomas Jefferson's secret love child or Grover Cleveland's out-of-wedlock offspring (both won elections despite the stories, which in Jefferson's case were very likely true).

But it has become a truism that in their modern, Internet-driven form, these persistent narratives spread far faster and run deeper than ever. And they share an unexpected trait: Most of the time, Democrats (or liberals) are the ones under attack. Yes, George W. Bush had some whoppers told about him -- such as his alleged scoffing that the French "don't have a word for 'entrepreneur' " -- but when it comes to generating and sustaining specious and shocking stories, there's no contest. The majority of the junk comes from the right, aimed at the left.

We're not talking here about verifiably inaccurate statements from the mouths of politicians and party leaders. There's plenty of that from all sides. And almost all of those statements are out in the open, where they get called out relatively quickly by the opposition or the mainstream media.

Instead, it's the sub rosa campaigns of vilification, the can-you-believe-this beauts that land periodically in your inbox from a trusted friend or relative amid the noise of every political season.

This sort of buzz occurs out of earshot of the news media. It gains rapid and broad circulation by being passed from hand to hand, from friend to relative to co-worker. Its power and credibility come from its source. Aunt Sally isn't just some reporter or anchor; she's a dear family member. You know her. She wouldn't lie to you, would she?

Viral emails didn't really come into widespread use until early in the past decade, says David Emery, who tracks urban legends for About.com. The first big target was a Democrat: presidential candidate John Kerry, subjected to wild claims about his wealth, his service in Vietnam and the supposed radical connections of his wife, Teresa Heinz Kerry.

Nonpartisan debunkers such as FactCheck.org, Snopes.com, PolitiFact.com, Emery and The Washington Post's Fact Checker have been chasing down these tales and dousing them like three-alarm fires for years. (There's even a chain email that paints Snopes as a liberal cover-up for the White House.) It's often difficult for these myth-busters to say with certainty where a falsehood began. But the numbers are clear.

Of the 79 chain emails about national politics deemed false by PolitiFact since 2007, only four were aimed at Republicans. Almost all of the rest concern Obama or other Democrats. The claims range from daffy (the White House renaming Christmas trees as "holiday trees") to serious (the health-care law granting all illegal immigrants free care).

Snopes turned up 46 viral emails regarding Bush during his eight years in office. By contrast, in just four years as a candidate and as president, Obama has been the subject of 100 such chain emails. The difference is not just in number but in kind: Twenty of the 46 Bush emails checked by Snopes turned out to be true, and many of these flattered or praised him. Only 10 emails about Obama have been true, and almost every one of them has been negative.

Emery estimates that more than 80 percent of the political emails that he's vetted over the past decade were written from a conservative point of view. "The use of forwarded email to spread 'false information' around is overwhelmingly a right-wing phenomenon," he said.

Rep. Nancy Pelosi, D-Calif., was a frequent target of chain emailers when she was speaker of the House, recalls Snopes founder David Mikkelson. But he can't recall a single urban myth about her successor, Rep. John Boehner, R-Ohio. Even former Alaska governor Sarah Palin, who inspires apoplexy among liberals, hasn't rated much on the email circuit since her stint as Sen. John McCain's running mate in 2008.

So are conservatives just more careless in their accusations, or more ruthless about spreading them, than liberals? Do conservative haters just like email more than their liberal counterparts? Is this part of what liberals deride as the "right-wing noise machine"?

Political scholar Kathleen Hall Jamieson notes that conservatives have always been the earliest adopters of new technologies, from direct-mail fundraising to sophisticated polling to the Internet. The viral email, she suggests, is just another techno-adaptation by the right.

But that would imply that liberals haven't figured out how to create their own viral email chains and that the conservative emails are part of some organized communications strategy. Jamieson concedes that there's no evidence for either of those conclusions.

Changes in the news media landscape have also helped lies to thrive. A generation or more ago, powerful gatekeepers -- large newspapers, broadcast networks, a news magazine or two -- dominated the dissemination of national news. No more.

"There was a mainstream media that acted as a filter," says Bill Adair, the editor of PolitiFact. Now, the filter is overwhelmed. "The Internet is a megaphone that spreads conspiracies quickly before there's anyone to correct the facts," he says. "There's no one between your crazy uncle and his address book."

Perhaps the best theory comes from Ari Fleischer, who served as Bush's first press secretary. Fleischer points out that conservatives traditionally mistrust mainstream news. Email is another way for them to put out their own messages, countering the perceived biases of traditional media sources, he says. "If you believe the liberal media is covering up," Fleischer explains, then you might be more susceptible to believe and pass on an outrageous email.

In fact, one version of the email that falsely cites big increases in Medicare premiums implicitly blames the media for obscuring the truth. "For those of you who are on Medicare, read the article below," it begins. "It's a short but important article that you probably haven't heard about in the mainstream news."

I suppose mainstream news outlets could simply ignore false stories, thus withholding legitimacy from them. But that wouldn't keep them from spreading. And playing dumb isn't an option when prominent people encourage speculation. Boehner, former Arkansas Republican governor Mike Huckabee and, most egregiously, Donald Trump, for example, all gave varying support to the "birther" story until Obama released his birth certificate. (And Texas Gov. Rick Perry has tried to keep the issue alive even after that.) The media covered what they said because their comments were newsworthy.

In the end, the only known cure for whisper campaigns that trample the facts is a massive dose of accurate and timely information. The truth is out there. You just have to want to find it -- and spread it around.

Paul Farhi writes for The Washington Post.

