Author Ed Klein has published hundreds of pages of attacks on President Bill Clinton and his wife, Hillary Clinton.

On Monday, as Klein's latest "exposé" of the former first family topped Hillary's memoir on the best-seller list, a source close to the Clintons fired back with a scathing, lengthy email to Business Insider blasting Klein as a pathological liar.

"This might sound hyperbolic, but there is no bigger liar in the entire world," the source said of Klein. "Lying isn't even the word for it. It's some kind of sickness where every single thing you write is fabricated. Every. Single. Thing. I mean, even the photos in his book were found to be altered."

Klein, who made headlines last weekend with a questionable article in Sunday's New York Post in which he claimed President Obama is backing Massachusetts Sen. Elizabeth Warren rather than Hillary Clinton in the 2016 presidential election, would not discuss criticism of his work when Business Insider called him Monday. Instead, he repeatedly referred us to his publicist, Jeremy Little, who provided us with a three-sentence statement from Klein defending his reporting.

"In typical Clinton fashion, when people can’t handle or respond to the truth, they attack the messenger," Klein said.

Klein also cited a Wall Street Journal report published Monday that described Hillary Clinton, who is widely viewed as the Democratic frontrunner for 2016, distancing herself from some of the Obama administration's policies. He implied this proved his claim Obama "has quietly promised Massachusetts Sen. Elizabeth Warren complete support if she runs for president."

"Reports surfaced this morning that Hillary Clinton is deliberately separating herself from the Obamas and their agenda. This is why, as I reported yesterday in the New York Post, the Obamas are searching for a new candidate for 2016 who is willing to carry on their legacy," Klein said.

However, there is a long history of alleged factual issues in Klein's work. As the source close to the Clintons noted, a photographer released evidence showing Klein misrepresented a salaciously cropped photo of President Clinton in his 2005 book, "The Truth About Hillary." That's just one of many problems that emerged from the book where Klein cast Hillary Clinton as "the most polarizing figure in American politics."

The Clinton confidant described Klein's writing about Hillary as "creepy."

"We have had to contend with all sorts of dastardly characters over the years, being a bad actor isn't unique in this business. But there is a special circle of hell reserved for his combination of pathological lying, hate, and just flat out creepiness," the source said of Klein, adding: "But he's got a good gig. He sits in his creepy lair and once every few years bangs out another pack of lies, doesn't have to bother with any nettlesome issues that get in the way, like sources or facts."

After writing "The Truth About Hillary," Klein moved on to President Obama.

Klein coauthored "The Obama Identity" in 2010. It was a fictional work that delved into the widely debunked conspiracy theories about Obama's birthplace. In 2012, Klein released "The Amateur," which attempted to expose Obama as "a callow, thin-skinned, arrogant president with messianic dreams of grandeur supported by a cast of true-believers, all of them united by leftist politics and an amateurish understanding of executive leadership." New York Magazine subsequently found an error on the book's very first page.

In addition to specific factual errors, Klein's political books have been widely criticized for their widespread reliance on anonymous sources to provide detailed behind-the-scenes stories from Obama and the Clintons' inner circles. These accounts have included shocking revelations and conversations that people on all sides of the political spectrum have described as improbable.

Klein's latest book, "Blood Feud," purports to reveal "the mutual loathing" that he claims exists between Obama and Hillary Clinton, the president's former secretary of state. Multiple close Obama allies did not respond to requests for comment on Klein, including Valerie Jarrett, the senior White House adviser Klein claimed was leading the "full-court press" to convince Warren to challenge Hillary Clinton in 2016. An aide to Jarrett responded to an email from Business Insider by pointing to comments White House press secretary Josh Earnest made about Klein's claims Obama was pushing Warren to run for president.

"At this point it’s still in the middle of 2014," Earnest said. "I’m not aware of any particular positions or candidates — or all that much thinking, to be honest with you — that the president has done as it relates to the next presidential elections. I haven’t actually seen those reports."

Earnest may not have seen reports based on Klein's claims, but they have been generating substantial media coverage. However, the source close to the Clintons argued Klein doesn't get as much attention as he did when he wrote his first book about Hillary.

"On it getting traction, I don't think he gets much anymore. When he did this in 05 people thought, Wow, he's a former NYT Magazine editor, he's reputable. It was a real fight to keep him off mainstream air," the source explained. "But as soon as people read any of it, it was absurd. I mean, he contends that Chelsea Clinton was conceived in a rape. He'll claim he didn't say that, but go back and read the chapter. It is nothing short of despicable."

The questions raised about Klein's work over the years do seem to have affected his standing in the mainstream media. In April, BuzzFeed reported the major publishing house HarperCollins terminated its contract with Klein because of concerns about his reporting. Both "The Amateur" and "Blood Feud" were published by a smaller, conservative publishing house, Regnery. In addition to his past roles as an editor at Newsweek and the New York Times Magazine in the 1970s and '80s, Klein has been a contributing editor at Vanity Fair, which excerpted both "The Truth About Hillary" and "The Obama Identity." Vanity Fair spokeswoman Beth Kseniak told Business Insider that while Klein is still with the magazine "we are not excerpting Ed's current book."

Edward Klein. EdwardKlein.com According to the Clinton source who emailed Business Insider, Hillary's team was unaware of "Blood Feud" until it came out because Klein made no effort to contact them during the course of his reporting. They also said no one in Hillary's inner circle reached out to her to report being approached by Klein about the book.

"In terms of contacting us, no, he hasn't. But that's neither here or there. What's amazing is that when people work on anything, a story, a documentary, a book, you hear from SOMEONE who checks in and say, Hey, I got a call from this guy Ed Klein, are you guys cooperating with him, should I talk to him?" the source said. "In this case, not one person. Not a single solitary human being. Didn't know about the book until it came out."

The source described this apparent lack of effort by Klein to contact Hillary's team and allies as proof his new book is fabricated.

"Do you know how hard that is?" the source said of the fact they heard from no one who spoke to Klein. "It's impossible. UNLESS you are fabricating every word, in which case you don't need to talk to anyone. Which is why he didn't. I haven't even looked at the book, but I'd be curious who he quoted and whether it was an interview or if the sourcing indicates that it's taken from the public record."

Klein and his publicist did not respond to questions from Business Insider about whether he attempted to contact Hillary's team and whether this called his work into question.

The Clinton source concluded with a blunt assessment of Klein:

"I'll end by saying the same thing I started with: there is no one anywhere near this despicable. Nobody."