SUMMARY: Since we published Obama's birth certificate, questions about its authenticity have been frequent and fierce. After reviewing the evidence, we're confident in our rulings.

It started as a whisper, a trickle of nagging doubt.

“As a concerned citizen, I’m wondering if there isn’t something fishy going on with the Obama certificate.”

“I have serious doubts about the purported 'birth certificate’ you were sent.”

“Something doesn’t smell right.”

Soon, e-mails and blog posts were flying. As the pace quickened, the tone sharpened.

“You should be apologizing ... for your misinformation regarding BO bogus birth certificate, that you claimed was genuine!”

At full throttle, the accusations are explosive and unrelenting, the writers emboldened by the anonymity and reach of the Internet.

And you can’t help but ask: How do you prove something to people who come to the facts believing, out of fear or hatred or maybe just partisanship, that they’re being tricked?

Sen. Barack Obama’s birth certificate is a document PolitiFact.com had sought for months. Countless chain e-mails, seeking to paint him as a secret Muslim, speculated that his full name included Muhammed (or Mohammed). Some said he is not an American citizen.

As a fact-checking news Web site, we went to extensive lengths to sort out the truth. We got a copy of his 1992 marriage certificate from the Cook County (Ill.) Bureau of Vital Statistics. His driver’s license record from the Illinois Secretary of State’s office. His registration and disciplinary record with the Attorney Registration & Disciplinary Commission of the Supreme Court of Illinois. Not to mention all of his property records.

Not one of these documents shows a Muhammed (or Mohammed) in Obama's name. They all read "Barack H. Obama" or "Barack Hussein Obama."

The ultimate document we sought was Obama’s birth certificate. Unlike the other documents, Hawaii birth certificates aren’t public record. Only family members can request copies, so when the campaign declined to give us one, we were stalled.

On June 13, 2008, Obama’s campaign finally released a copy, while launching a fact-check Web site of its own, Fightthesmears.com. The site is a direct response to allegations about Obama that won’t go away: He’s Muslim. He took the oath of office on a Koran. He refuses to say the Pledge of Allegiance. PolitiFact has researched all of these accusations and none of them are true.

When the birth certificate arrived from the Obama campaign it confirmed his name as the other documents already showed it. Still, we took an extra step: We e-mailed it to the Hawaii Department of Health, which maintains such records, to ask if it was real.

“It’s a valid Hawaii state birth certificate,” spokesman Janice Okubo told us.

Then the firestorm started.

• Where is the embossed seal and the registrar’s signature?

• Comparing it to other Hawaii birth certificates, the color shade is different.

• Isn’t the date stamp bleeding through the back of the document “June 2007?” (Odd since it was supposedly released in June 2008.)

• There’s no crease from being folded and mailed.

• It’s clearly Photoshopped and a wholesale fraud.

At PolitiFact.com, we’re all about original sources. We don’t take anyone at their word or take the reporting of other media organizations as proof. We go to the heart of the story, the source of the truth — original, corroborating documents.

When the official documents were questioned, we went looking for more answers. We circled back to the Department of Health, had a newsroom colleague bring in her own Hawaii birth certificate to see if it looks the same (it’s identical). But every answer triggered more questions.

And soon enough, after going to every length possible to confirm the birth certificate’s authenticity, you start asking, what is reasonable here?

Because if this document is forged, then they all are.

If this document is forged, a U.S. senator and his presidential campaign have perpetrated a vast, long-term fraud. They have done it with conspiring officials at the Hawaii Department of Health, the Cook County (Ill.) Bureau of Vital Statistics, the Illinois Secretary of State’s office, the Attorney Registration & Disciplinary Commission of the Supreme Court of Illinois and many other government agencies.

Sounds like a Vince Flynn novel.

Peter Goelz knows a little something about conspiracy theorists.

He was managing director of the National Transportation Safety Board in 1996 when TWA Flight 800 crashed off Long Island, killing 230 people. While the NTSB’s investigation found no evidence of sabotage or terrorism, the Internet was stocked with insistent accusations.

“We were right at the beginning of this Internet lunacy,” Goelz said in an interview with PolitiFact. “And there were a variety of crackpot Web sites and Web commentators that generated all sorts of rumors. The principle one was that TWA in fact was shot down by an errant Navy missile in ... a live-fire exercise off the Hamptons.”

Nine miles off Long Island, in the middle of summer. And then a full-scale coverup by the Navy and all the sailors involved.

“I am sure that we spent another $10-million, perhaps $20-million, out of a $50-million investigation, to just knock down and put to bed these kinds of rumors, these insidious rumors,” Goelz said. “We felt like we had to answer every question because it was such a public and dreadful and confounding event.”

Goelz, who is now a communications consultant in Washington, D.C., says the Internet has given a platform to anyone to say anything. And a way to find others who want to hear it.

“Online, they can be almost anything,” he said. “They can be the crusading investigators that they always wanted to be.”

The Hawaii Department of Health receives about a dozen e-mail inquiries a day about Obama’s birth certificate, spokesman Okubo said.

“I guess the big issue that’s being raised is the lack of an embossed seal and a signature,” Okubo said, pointing out that in Hawaii, both those things are on the back of the document. “Because they scanned the front … you wouldn’t see those things.”

Okubo says she got a copy of her own birth certificate last year and it is identical to the Obama one we received.

And about the copy we e-mailed her for verification? “When we looked at that image you guys sent us, our registrar, he thought he could see pieces of the embossed image through it.”

Still, she acknowledges: “I don’t know that it’s possible for us to even say beyond a doubt what the image on the site represents.”

And there’s the rub. It is possible that Obama conspired his way to the precipice of the world’s biggest job, involving a vast network of people and government agencies over decades of lies. Anything’s possible.

But step back and look at the overwhelming evidence to the contrary and your sense of what’s reasonable has to take over.

There is not one shred of evidence to disprove PolitiFact’s conclusion that the candidate’s name is Barack Hussein Obama, or to support allegations that the birth certificate he released isn’t authentic.

And that’s true no matter how many people cling to some hint of doubt and use the Internet to fuel their innate sense of distrust.