All day, TVNewser has been making calls on the story of Martin Eisenstadt, trying to find out if the person who claims to be one of the sources of Carl Cameron's reporting about Gov. Sarah Palin's is real.

On his Website, Eisenstadt claims he was one of Cameron's sources: "Last week I was the one who leaked those things to a producer at Fox News who works with Cameron. Carl and his producers are good guys, and I don't want them to have to worry about protecting their sources," he wrote.

And that may have been enough for MSNBC. During a segment yesterday, David Shuster discussed Eisenstadt. Shuster began the segment saying, "We now have a face and a name with these allegations." But minutes later, Shuster wasn't so sure:

There is something suspicious about this blog that we had printed out. I'm not sure we can necessarily say this is in fact who this person is because I've never heard of the name Martin Eisenstadt and there's now indications that maybe this was just made up.

But if MSNBC was duped, so, apparently, were many others. CBS News has linked to an Eisenstadt post before, in which he claims Joe the Plumber has ties to Charles Keating. The Huffington Post as well as the LA Times may have been taken for a ride over an Eisenstadt story claiming Paris Hilton's parents were miffed at the McCain campaign for using the socialite in a campaign ad.

So who is he? His bio claims: "Mr. Eisenstadt sits on five editorial boards, has testified before many congressional committees, and worked on five presidential campaigns." Including, apparently, the McCain campaign.

Through the course of several emails with Eisenstadt today, here is what he had to say:

It's strange for me (and all a bit Hegelian) to get requests to prove that I exist. But I appreciate your journalistic responsibility to do so. I'm not sure if you saw the update I posted on my blog where I address the issue head on. In short, every single blog that says I am a "hoax" has emanated from a single, bitter individual who for some reason has a vendetta against me - a golf blogger allegedly named "Wolfrum." You see, in the Google era it is very easy to spread rumors about people. You'll see in that post some links to youtube clips from both the BBC, and our own institute wherein I refute these claims on camera. I've yet to see any of my "accusers" show their face on camera.

You flatter me that I could construct such an elaborate ruse! I suppose if I didn't exist, it would indeed be impressive to have made all this up. In the meantime, my attorneys have advised me not to get into any details about my discussions with Fox News, Carl Cameron or any of his producers or FNC staff. You can see what happened to Scooter Libby when he started leaking things, so I can't take any further risks.

So, the mystery, for now, continues.

Click continued to see the MSNBC clip yesterday as well as one of the "proof" YouTube videos offered by Eisenstadt...