When Carter Page was named as one of Donald Trump's foreign policy advisers during the 2016 US presidential election campaign, the head of Mr Trump's foreign policy team had never heard of him.

The energy consultant and banker had spent three years working in Moscow for US bank Merrill Lynch, but was virtually unknown in Washington political circles.

Now Dr Page is one of the most infamous names caught up in Operation Crossfire Hurricane — the FBI's investigation opened in secret during the 2016 election campaign, examining the Trump campaign's ties to Russia and allegations of collusion and Russian meddling.

Dr Page told Four Corners he was an "innocent victim of a conspiracy theory".

"It's similar to the Salem witch trials many centuries ago. In every way it's a witch hunt. There is zero basis for anything related to the controversy surrounding myself," he said.

The former director of national security for the Trump campaign, JD Gordon rues the day he met Dr Page.

"Carter Page fell right into the trap," he said.

James Clapper, Barack Obama's director of national intelligence said Dr Page's intentions were still unclear.

"Not sure I can sort him out in my own mind whether he was doing something nefarious or was just naive. I don't know," he said.

"But I do know that he was a matter of concern to the FBI since he was on their scope since about 2013 for his interactions with known Russian operatives."

Plucked from obscurity
Early in the campaign, Republican candidate Mr Trump had been criticised for his lack of foreign policy experience.

In March 2016, Mr Trump was asked by the Washington Post to name his foreign policy advisory team. Included on the list of names rattled off by the future president was "Carter Page, PhD".

JD Gordon was taken aback by the appointment.

"We did not know who he was," he said.

Dr Page said he was chosen after getting in touch with an old friend.

"The Chairman of the Republican Party here in New York is someone who I had known for many years, and so I had mentioned my interest and he introduced me to the campaign," he said.

But with no opportunity to thoroughly vet their new addition, the foreign policy advisory team and senior campaign leadership were unaware that Dr Page was already well known to US intelligence agencies.

Groomed by Russian spies
In January 2013, Dr Page had met a Russian man who he believed was a young diplomat.

"We had a chitchat, no big deal. We sort of stayed in touch, exchanged cards. I think we had one coffee one time," Dr Page said.

That man was Victor Podobnyy, a Russian spy who was actively trying to cultivate intelligence sources within the US.

Dr Page and Podobnyy communicated for six months over text and email, with Dr Page passing the Russian spy publicly available information about the energy market.

Dr Page maintains he did nothing wrong in these interactions.

"If you talk about intelligence gathering, let's just put it this way: it was at a much lower level than my average student sitting in my classroom at NYU. So if this is intelligence gathering, then okay. But this is just making a case out of nothing," he said.

In June 2013, the FBI who had been monitoring the spies, stepped in and called Dr Page to a meeting. They informed him of Podobnyy's identity and motive.

Dr Page insisted to Four Corners he was not shocked by the FBI's news.

"Surprise? No, not really. People reach out to me, and I'm happy to help. I like talking about substantive matters and helping where I can," he said.

"It was this little sideshow that they decided to run with. He never cultivated anything as an asset."

Dan Hoffman was one of America's top spies and the former CIA station chief in Moscow.

He recognises these interactions as common to the tradecraft of Russian agents.

"Typically, when Russian intelligence is in contact with someone, they don't waste their time. They have a reason for doing it," he said.

"Sometimes they'll spot someone who looks like they might be potentially of some interest and they'll take a look at them and see whether the person has interesting access."

Victor Podobnyy and Igor Sporyshev were charged with espionage in January 2015 but had diplomatic cover and were allowed to leave the US.

Dr Page was never accused of any wrongdoing but was now well and truly on the radar of the FBI.

Russian connections
In July 2016, three months after being named as one of Mr Trump's election campaign foreign policy advisers, Dr Page was selected by Russian officials to give a speech at the New Economics School in Moscow.

"I'd spoken at a lot of the top universities in Moscow countless times before over the years, and I was offered, invited to come then. I mentioned it to a few people and people said, 'If you want to do this, this is something that you're doing on your own'. That was the end of that," he said.

JD Gordon advised Dr Page not to accept the invitation.

"I thought it would reflect poorly on the campaign, and it would generate a lot of negative publicity. He eventually went around me to the campaign chairman and got permission anyway, and he went. We've been paying the price since then," he said.

Dr Page's speech criticised US policy towards Russia as too harsh. At the time US media picked up on him attacking Washington's focus on "ideas such as democratisation, inequality and corruption".

But what is still being examined almost two years later is the interactions and meetings Dr Page had on that trip.

On his journey home, Dr Page emailed the Trump campaign, boasting of the high-level contacts he had made in Moscow.

"I'll send you guys a readout soon regarding some incredible insights and outreach I've received from a few Russian legislators and senior members of the presidential administration here," he wrote.

This email has since fuelled speculation that there was something more going on than a simple speech.

The Steele dossier
According to a raw, untested intelligence dossier compiled by former MI6 agent Christopher Steele, Dr Page had held secret meetings with senior Kremlin officials and businessmen in Moscow.

Mr Steele's dossier alleges Dr Page was used as an intermediary, as part of "a well-developed conspiracy of cooperation" between the Trump campaign and Russian leadership.

Veteran Washington reporter Michael Isikoff was briefed by the former British spy in September 2016.

"[Steele] told me that Page had meetings in Moscow in which he discussed the Trump campaign and help that the Russians could provide the Trump campaign, in exchange for which Trump would be favourably disposed to lift sanctions on Russia," he said.

"What really got my attention was he said that he had reported this to the FBI because he believed it was a national security matter."

Mr Steele's sources specifically alleged Dr Page had met with Igor Sechin — the head of Russian oil giant Rosneft. Mr Sechin's interest in sanctions was personal, he was explicitly targeted by US sanctions on Russia and banned from US travel.

Dr Page has repeatedly denied meeting Mr Sechin but under oath to a congressional committee investigating Trump campaign ties to Russia, he conceded he had met with another Rosneft official, Andrey Baranov.

"This is someone who I'd known for about a decade or so, over a decade, and I saw him. We went to a party to watch the Euro Cup football match."

Four Corners asked Dr Page directly if he had any conversations about sanctions with Andrey Baranov.

"Look, sanctions is a topic that people in the economy talk about at some point. Did it possibly come up? I have no recollection. I have no idea. It may have been a couple of words in passing," he said.

Isikoff says Dr Page's story about his interactions on this Moscow trip keeps shifting.

"It's interesting because Page denied everything, just sort of sweeping, this is all nonsense, nothing like this is true," he said.

"When he finally was forced to testify before the House Intelligence Committee, turns out that those denials were not quite as airtight as he initially suggested.

"It does suggest that there was something real that Steele was picking up on."

'An ill-advised trip'
In late September 2016 news that the FBI was investigating Dr Page's trip to Russia broke in the US media

Dr Page was the first Trump campaign member to be publicly linked to allegations of Russian collusion.

He was denounced by Mr Trump's team and forced to leave the campaign.

JD Gordon told Four Corners it was deeply embarrassing and damaging.

"He made an ill-advised trip that the Democrats in Barack Obama's administration seized upon," he said.

"And deep state folks like James Comey, they latched onto this piece of evidence to say, 'Oh ho! There could be collusion, Carter Page!'"

Dr Page was investigated by the FBI but has not been charged with any offence.

He was placed under FBI surveillance from October 2016 for almost a year, a move he claims was made to allow US officials to spy on the Trump campaign.

Dr Page insists the FBI's "Operation Crossfire Hurricane" is storm in a teacup.

"I am just a sacrificial lamb for people that are just looking to create a false story to tear down the Trump campaign," he said.