Donald Trump's business dealings with a white-collar criminal allegedly tied to organized crime are beginning to percolate up into the 2016 presidential campaign.

The real estate magnate's blunt demeanor, suggesting an executive who ruthlessly gets his way, is part of his appeal to some voters. But his past business dealings are also darkened by ties to a convicted criminal and by the shadow of the Mafia.

Felix Sater (Screenshot)

Felix Sater, a fraudster with alleged connections to Cosa Nostra, worked closely with Trump on numerous occasions. His ties to the mob have been documented by the New York Times, BBC, and other news organizations, and largely revolve around his involvement in a money-laundering scheme dating to the 1990s.

The Times reported that Sater "sought protection and help from members of the Mafia in resolving disputes with 'pump and dump' firms operated by other organized crime groups." The paper cited a specific example from 1995, when Sater reportedly used a "soldier in the Genovese crime family" to resolve a conflict Sater had with a member of the Gambino crime family.

Mark Mitchell, a reporter for Deep Capture who formerly worked for the Wall Street Journal and TIME, began investigating Sater ten years ago. He told the Washington Examiner that Sater, "would definitely be somebody [Trump] shouldn't be doing business with."

But in an interview with the Examiner, Sater rattled off the projects he and Trump worked on together — Trump SoHo, Trump International Hotel and Residence Phoenix, Trump International Hotel and Residence Ft. Lauderdale — and talked about traveling with "The Donald" to Denver for a never-completed project. Sater wished Trump well and said, "He will probably make the best president ever because of his acumen and intelligence and ability to get things done."

In 2009, a federal judge sentenced Sater for his role in a stock fraud and money-laundering scheme during the mid-1990s. Despite Sater's agreement to having owed $60 million in restitution to victims of his crime, the judge handed Sater a $25,000 fine after Sater's cooperation with the federal government on other matters.

Attorney General Loretta Lynch, formerly the U.S. Attorney for the Eastern District of New York, has said Sater worked with her office for more than a decade providing "valuable and sensitive information to the government." Little information about Sater's work with the government has been made public, but Lynch has stated that Sater's cooperation led to the convictions of more than 20 people, including members of the Cosa Nostra.

In a 2014 petition to the Supreme Court to release records from Sater's criminal case, attorney Fred Oberlander alleged that Sater continued to defraud new unsuspecting victims while the government concealed his previous crimes. The Supreme Court denied the petition for Writ of Certiorari.

"By 2002, [Sater] had infiltrated and largely controlled Bayrock, a New York developer with ties to organized crime, in the next several years using it to launder hundreds of millions, skim and extort millions more, and again swindle his investors and partners," the petition alleged. "[F]or example, fraudulently inducing banks to lend hundreds of millions to Bayrock by concealment fraud (hiding the material fact of his conviction from them), threatening to kill anyone at the firm he thought knew of the crimes committed there and might report it."

Also in 2002, Sater said, he began working with Trump. At least one of the projects Trump worked on with Sater has come under additional scrutiny. In 2010, Reuters reported, "Donald Trump and the promoters of his Trump SoHo hotel-condominium were sued by buyers who accused them of fraudulently touting out-sized sales figures to encourage them to buy units and inflate the financial project's health."

Sater said he worked as a senior adviser to Donald Trump in 2011, which is after his sentencing in the stock-fraud case, and after the lawsuit was filed against his and Trump's work on Trump SoHo. The lawsuit was settled in November 2011, and the buyers reportedly received 90 percent of their total deposits back. Sater's LinkedIn page also says he worked as a senior adviser to Donald Trump at the Trump organization during 2010 and 2011.

Trump has sought to distance himself from Sater. He walked out of an interview with the BBC in 2013 after the reporter asked about his decision not to maintain links with Sater. Before leaving, Trump told the BBC, "Sometimes we'll sign a deal and the partner isn't as good as we'd like."

Asked about Sater's relationship with Donald Trump, Corey Lewandowski, Trump's campaign manager, told the Examiner that Sater is not a "campaign employee" and has nothing to do with the campaign.

"I have no idea who Felix Sater is, he has nothing to do with the Donald J. Trump for President presidential campaign," Lewandowski said. "I've never heard of the guy and in the whole time you've raised it to me, he is in no way, shape, or form affiliated with the campaign."

Sater insists that he is "not a bad guy," despite the fraud case and having served time for allegedly stabbing a fellow Wall Street broker with the stem of a Margarita glass. Sater pointed to his work to purchase missiles on the black market, as evidence that he sought to protect the U.S., not harm its citizens. In The Scorpion and the Frog: High Times and High Crimes, Salvatore Lauria, an associate of Sater, wrote that Sater attempted to purchase the weapons from Osama bin Laden, as the New York Times has noted. Sater and Lauria were friends, and worked as partners at White Rock Partners, a brokerage firm.

"I'm not an arms dealer," Sater said. "I wasn't buying missiles for myself. We were trying to get missiles off the black market so they wouldn't be used against U.S. airliners. Buying missiles, in the things that I've done … it's one one-hundredth of the things that I've done, one one-hundredth of one percent."

Sater declined to provide evidence of his claims, and did not answer questions about links to Russian mobsters.

But Trump's ties to organized crime are deeper and longer lasting than just the recent past. Wayne Barrett, an investigative reporter who has covered Trump since the 1970s and authored Trump: The Deals and the Downfall, said Sater is just one of many mob associations that Trump and his father, Fred Trump, had throughout the years.

Barrett said as Trump rose in the business world he had a "special relationship" with known mobsters, and claimed that he would meet with "Fat Tony" Salerno, a boss of the Genovese crime family, in the office of Roy Cohn, a powerful New York attorney who represented both men.

"You could go from one end of his empire to another and find a mob connection at one or the other," Barrett said. "Some of it is unavoidable in the times in which [he worked]."

The Federalist recently claimed that Trump has ties to organized crime families from both Philadelphia and New York. A CNN report added that Trump appeared to have overpaid for property from a pair of Philadelphia mobsters dubbed the "Young Executioners" in the early 1980s.

But none of the allegations directed at Trump appear to be hampering his perch atop several national polls of Republican presidential candidates. The negative reaction to his controversial comments about illegal immigration and Arizona Sen. John McCain's military service has not thrown him off his game either.

As the first nationally televised presidential debate looms just a few days away, other presidential contenders' campaigns appear to be quietly gearing up for the worst in dealing with Trump.

"Imagine a NASCAR driver mentally preparing for a race knowing one of the drivers will be drunk," tweeted John Weaver, an adviser for Ohio Gov. John Kasich. "That's what preparing for this debate is like."

Some political insiders think Trump can turn his ties to the mob into better poll numbers, as he has with past controversies. Ford O'Connell, a GOP strategist and veteran of Sen. John McCain's 2008 presidential campaign, said he thinks Trump will try to leverage his mob connections as a reason why he should win the GOP nomination.

"As accusations grow about ties to organized crime, et cetera, it would not shock me if he turned this into a foreign policy credential," O'Connell said. "He literally says 'I've had success in dealing with unsavory people and sometimes you have to deal with these types of people if you want to get things done.' I can literally see him moving his little Tyrannosaurus rex arms saying that."

Barrett said he thinks Trump should no longer be taken seriously.

"I am a little stunned at the new Donald," Barrett said. "This is not at all the way he behaved before; until he got the TV show he was not a circus clown. … I think this descent into psychosis, it just gets worse — it doesn't get better."

"He's a Kardashian — a Kardashian without the cleavage."