Sidney Blumenthal
Sidney Blumenthal (C), a longtime Hillary Clinton friend who was an unofficial adviser while she was secretary of state, gave a deposition to the House Select Committee on Benghazi in Washington June 16, 2015 Reuters /Jonathan Ernst

Donald Trump says Hillary Clinton's old adviser Sidney Blumenthal started the false "birther" whisper campaign that President Obama was born in Kenya in 2008 and that Trump championed until just last month.

And again this week Blumenthal's name surfaced when Trump put words in the adviser's mouth. Mistakenly, he quoted from a Newsweek article forwarded to Clinton's campaign chairman John Podesta. The email, sent by Blumenthal, was then released by Wikileaks from a hacked account.

Trump claimed Blumenthal said the 2012 attack on the US embassy in Benghazi, Libya, was "almost certainly preventable". But, in truth, those were the words of Newsweek journalist Kurt Eichenwald who wrote the story.

So who is Sidney Blumenthal, and why does Trump heap such emphasis and importance on his words?

A July article in Vanity Fair called Blumenthal "a sort of 24-7 mini-mart of ideas for Clinton" after journalist James Warren combed through hundreds of emails from Clinton's private server and released by Wikileaks that were requested as an FOI. But Clinton's relationship with the adviser goes back much further – and may not be what Trump suggests today.

Bill Clinton and Blumenthal

Blumenthal is no stranger to the public eye. As a White House aide under Bill Clinton, he focused on media and communications because of his reporting at The Washington Post and The New Yorker. But Blumenthal first made headlines that he wasn't writing himself when Conservative Matt Drudge – who has filled in on Rush Limbaugh and Sean Hannity's radio shows – falsely accused him in 1997 of beating his wife, citing "top GOP operatives".

Blumenthal and his wife brought a $30m libel lawsuit against Drudge when he couldn't produce the court documents that he claimed would prove it.

Again, during the Monica Lewinsky scandal in the late 1990s, Blumenthal found himself at the centre of President Bill Clinton's impeachment trial in the Senate.

He was brought to testify before a grand jury relating to information he told journalists about independent prosecutor Kenneth Starr's team. The case against Bill Clinton was later dropped.

Hillary's adviser in 2008

Over the years Blumenthal has become a close aide and adviser to Hillary Clinton, yet has often been a magnet for controversy.

In September James Asher, the former Washington Bureau Chief of news source McClatchy, which operates 29 daily newspapers in 14 states, said that Blumenthal approached him at a Democratic primary in 2008.

"During that meeting, Mr. Blumenthal and I met together in my office and he strongly urged me to investigate the exact place of President Obama's birth, which he suggested was in Kenya," Asher wrote in an email to McClatchy. "We assigned a reporter to go to Kenya, and that reporter determined that the allegation was false."

An Iowa campaign worker also handed around information about the conspiracy and was quickly fired.

Benghazi and the 2016 election

In the past year an FOI release of hundreds of emails sent by Blumenthal to Hillary Clinton when she was Secretary of State has been released by Wikileaks. Vanity Fair's Warren calls these "by turns gossipy, fawning, and conspiratorial," but there is no hint of anything illegal or to suggest that Blumenthal was somehow involved in the Benghazi attack.

"Do you remember when Ambassador [Chris] Stevens in Benghazi was calling, and writing – they were desperate for help. They say like 600 times, right?" Trump told a booing crowd at a campaign stop in Pennsylvania Monday. "The only one she was speaking to is Sidney Blumenthal."

However, a search of Wikileaks emails at the time of the attack on September 11 and through the rest of the month after show only two emails with duplicate information sharing reaction to the Ambassador's death in Libya.

Sidney Blumenthal Wikileaks
A search of emails from Sidney Blumenthal during the 2012 Benghazi attack found in Wikileaks' searchable database of material from Hillary Clinton's server

It isn't clear how much a role Blumenthal has been playing in the current Clinton campaign, but fresh leaks from a hacked email account released by Wikileaks show less than a handful of emails from his address.

Clinton's campaign manager John Podesta seems to have a low opinion of the adviser, suggesting that he may be out of the Democratic nominee's closest circle.

"Sid is lost in his own web of conspiracies," Podesta wrote to a columnist in an email earlier this year. "I pay zero attention to what he says."