Donald Trump’s campaign chairman was a key player in multi-million-dollar business propositions with Russian and Ukrainian oligarchs — one of them a close Putin ally with alleged ties to organized crime — which foreign policy experts say raises questions about the pro-Russian bent of the Trump candidacy.

“The relationships that Trump’s advisors have had with pro-Russian forces are deeply disturbing,” said David Kramer, a former senior State Department official in the George W. Bush administration and a former adviser to Marco Rubio’s presidential campaign. “Trump’s attitude on Russia is not in line with most Republican foreign-policy thinking. Trump has staked out views that are really on the fringe.”

In 2008, according to court records, senior Trump aide Paul Manafort's firm was involved with a Ukrainian oligarch named Dmytro Firtash in a plan to redevelop a famous New York hotel, the Drake. The total value of the project was $850 million. Firtash’s company planned to invest over $100 million, the records say.

That same year, Firtash acknowledged to the U.S. ambassador in Ukraine that he got his start in business with the permission of a notorious Russian crime lord, according to a classified State Department cable. Other cables say Firtash made part of his fortune through sweetheart natural gas deals between Russia and the Ukraine.

Around the same time, companies controlled by another Russian billionaire, Oleg Deripaska, paid $7.35 million toward management fees for Manafort and his partners in connection with an investment fund, according to a court filing in the Cayman Islands. Deripaska once was denied entry to the United States because of alleged mafia ties, current and former officials told NBC News. Deripaska is considered by U.S. officials to be among Putin’s inner circle.

The Drake deal didn’t go through, and the Deripaska investment arrangement ended in a dispute. But Manafort’s dealings with Firtash and Deripaska, documented in court records obtained by NBC News, are among several the political operative has maintained with wealthy Russian and Ukrainian businessmen going back over eight years. Firtash is a wanted man, indicted by the Justice Department in 2014 over bribery allegations in India. He is living in exile in Austria.

Republican presidential candidate Donald Trump with campaign chair Paul Manafort (right) and daughter Ivanka Trump. Bill Clark / CQ-Roll Call, Inc.

Now, Manafort is helping to run what foreign policy experts say is the most pro-Russian political campaign in modern American history. Many observers are wondering whether Manafort’s financial dealings with a Putin ally and a wealthy Ukrainian have anything do with Trump’s pro-Putin tilt.

“It’s just extraordinary,” said Michael McFaul, a former U.S. ambassador to Russia under President Barack Obama. “This is not a Republican or Democratic thing. Almost nobody agrees with Trump on this stuff.”

Trump reshuffled his campaign Tuesday, bringing in Stephen Bannon, who runs the conservative Breitbart News website, as chief executive. But Manafort retains the title of chairman.

In interviews and statements to NBC News, Manafort says he “never had a business relationship” with Firtash. “There was one occasion where an opportunity was explored. ... Nothing transpired and no business relationship was ever implemented.”

On the political front, Manafort was paid handsome sums for years to advise a pro-Putin Ukrainian political figure, Viktor Yanukovych, who fled to Russia in 2014 after he was ousted as president in a political revolution. U.S. officials say Yanukovych was deeply corrupt and did Putin’s bidding in Ukraine. Manafort met regularly with the U.S. Ambassador in Kiev, William Taylor, according to a source familiar with the meetings.

Russian President Vladimir Putin speaks with Oleg Deripaska at the International Investment Forum in Sochi, 2008. ILIA PITALEV / AFP-Getty Images file

Deripaska was a Yanukovych backer who is considered by U.S. officials to be among Putin’s inner circle of billionaire businessmen.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Manafort told NBC News’ Hallie Jackson he hasn’t had dealings with Deripaska for four years, and he denies that there was anything inappropriate about their dealings.

Four years after Republican Mitt Romney in 2012 called Russia America’s greatest geopolitical foe, Trump says he sees the word much differently. He has suggested he might accept Russia’s seizure of Ukraine’s Crimea region. He has questioned whether the U.S. would defend the Baltic States against a Russian attack. He has praised Putin as "bright and talented."

According to reports by the Washington Post and other publications, the Trump campaign’s only change to the GOP platform was softening a plank calling for lethal assistance to help Ukraine roll back the Russian invasion. An allegation Manafort denied in an interview on NBC’s Meet The Press.

Just this week, Trump promised to work with Russian against ISIS, a sentiment that is met with skepticism by intelligence experts who say Russia has been undermining U.S. efforts to end the Syrian civil war.

Regarding his political consulting, Manafort said: "I've never dealt with the Russian government, I've never had a relationship with the Russian government," adding later, "As I've said many times Yanukovych was a pro-Western, not pro-Putin, president.”

Current and former American officials call that claim laughable. Manafort may have tried to steer Yanukovych in a pro-Western direction, they say, but he wasn’t successful.

Yanukovych "came to power through democratic means but then he quickly engaged in massive corruption deals with the Russians that were deeply adverse to Ukraine’s interest," Kramer said. "And then in February of 2014 he launched a bloody crackdown on protesters in Mydan that killed a hundred people. So we're talking about an official in Ukraine who has blood on his hands, who is up to his eyeballs in corruption — and Manafort was advising and working for him.”

It’s unclear how much Manafort was paid to advise Yanukovych and his political party. Manafort did not register with the Justice Department as a foreign lobbyist, nor is it clear if he was required to do so.

Also unknown is how much money the wealthy Manafort made through his relationships with Yanukovych allies, including Firtash and Deripaska.

Ukrainian oligarch Dmytro Firtash waits for the start of his trial at the main court in Vienna, Austria, April 30, 2015. Ronald Zak / AP file

Court records offer a glimpse of the Trump adviser’s dealings.

According to court documents and diplomatic cables, Firtash’s fortunes have been largely built on having set up a company to “skim” hundreds of millions of dollars of natural gas sales between Russia and Ukraine. That was well known to anyone who operated in Ukraine at the time, current and former officials say.

"His success was built on remarkable sweetheart deals brokered by associates of Russian leader Vladimir Putin, at immense cost to Russian taxpayers," according to a 2014 investigation by the Reuters news agency.

A letter addressed to Manafort from one of Firtash’s representatives said Firtash’s company was "prepared to provide $112 million in equity for the [Drake hotel redevelopment] project." One of the other partners working with Manafort on the deal was the former exclusive broker for Fred Trump's properties, Brad Zackson. Fred Trump is the now-deceased father of Donald Trump.

The documents were filed in a lawsuit by the former Ukrainian prime minister, Yulia Tymoshenko, in 2011. The lawsuit was dismissed on three separate occasions in federal court. The judge ruled most recently that Tymoshenko and the other plaintiffs failed to establish the predicate acts necessary to establish that there was racketeering in the case.

Documents contained in that lawsuit show that Manafort and his partners were meeting with Firtash to setup the investment in the Drake project. Eventually, documents show, Firtash’s investment company transferred $25 million into escrow to further the project along.

In other documents, a management fee payment to Manafort, Zackson, and their partners from Firtash were discussed. "Basically, DF is still totally on board and a wire will be forthcoming either the end of this week or next week as a partial payment on the 1.5," Manafort said in an email to Brad Zackson, his partner in the deal, on June 8, 2009. DF is Firtash, and 1.5 referred to a $1.5 million fee payment, according to court documents.

In 2008, according to a State Department cable posted by WikiLeaks, Firtash told U.S. Ambassador William Taylor that he got his start in business with the permission of one of Russia’s most well-known organized crime bosses, Semion Mogilevich. But Firtash claimed he was forced to deal with such people.

Semion Mogilevich FBI

"He was adamant that he had not committed a single crime when building his business empire," the cable says, and he "argued that outsiders still failed to understand the period of lawlessness that reigned in Ukraine after the collapse of the Soviet Union."

At one point during the meeting, Firtash began to talk about "mistakes he might have made," the cable says, but was waved off by an accompanying adviser.

Mogilevich was once on the FBI’s top 10 most wanted list, has an Interpol Red Notice out for his arrest, and the FBI says publicly he is "involved in weapons trafficking, contract murders, extortion, drug trafficking, and prostitution on an international scale." In a posting on the FBI’s website, the man who ran the investigation that eventually led to an indictment against Mogilevich said, "What makes him so dangerous is that he operates without borders."

In 2014, Firtash was charged by the Justice Department with paying $18.5 million in bribes in India to expand his business empire. Court papers say it was a racketeering conspiracy to sell titanium materials to Boeing for their newest jet, the 787. Last year, an Austrian judge refused to extradite him to the U.S.

Manafort’s business ties to Deripaska were detailed in a 2014 legal action in the Cayman Islands.

Deripaska had been repeatedly denied a visa to enter the United States over his alleged ties to organized crime, current and former officials tell NBC News. However, several officials tell NBC News he now has been given diplomatic status by the Russian government, allowing him to enter the U.S. with immunity.

In the Cayman Island court petition, a company controlled by Deripaska alleged it invested $18.9 million in 2008 in a firm in which Manafort had an interest, Pericles Emerging Markets, to acquire a company called Black Sea Cable. The petition also alleged companies controlled by Deripaska paid $7.35 million toward management fees for Manafort and his partners. The court filing was seeking an accounting of the money.

Manafort was questioned by Cayman Islands officials in the matter earlier this year, his lawyer has said publicly.

Manafort said that the matter was closed.