George Papadopoulos emailed powerful Trump campaign figures about Russian contacts The campaign adviser pleaded guilty to lying to the FBI about Russian contacts.

 -- Paul Manafort, Corey Lewandowski and Sam Clovis are among the Trump campaign officials who were contacted by George Papadopoulos, the low-level campaign adviser who lied to the FBI about his dealings with suspected Russian agents, sources familiar with the emails have told ABC News.

Documents unsealed by special counsel Robert Mueller on Monday detailing correspondence between Papadopoulos and a group of foreign nationals show that within weeks of being described by Trump as an important part of his national security team, Papadopoulos was in London meeting with people who said they could deliver “dirt” on rival candidate Hillary Clinton, including “thousands of e-mails.”

One of so-called “foreign contacts” is identified as a professor who introduced Papadopoulos to a Russian woman who claimed to be Vladimir Putin’s niece and a Russian Ministry of Foreign Affairs official.

This is the clearest evidence yet of possible collusion between the Trump campaign and the Russian government, but Sen. Richard Burr of North Carolina, the Republican chairman of the Senate Intelligence Committee, told ABC News these latest revelations prove nothing.

“If indictments were all about Russians reaching to Americans there would be a lot of people who would have been indicted yesterday,” Burr said.

Since the documents have been made public, Trump and his team have sought to minimize Papadopoulos’ role in the campaign, characterizing his involvement as “extremely limited.” Papadopoulos, however, appears to have had a direct line of contact to some of the campaign’s most powerful figures, which he used to discuss the possibility of a meeting between Trump and Russian President Vladimir Putin in Russia.

The sources told ABC News that one of the people identified in the Papadopoulos case as a high-ranking official is Paul Manafort, the onetime campaign chairman who forwarded one of Papadopoulos’ emails to another campaign official, Rick Gates, stating: “We need someone to communicate that DT is not doing these trips,” referring to a proposed trip to Russia. “It should be someone low level in the campaign so as not to send any signal.”

Lewandowski, the former campaign manager who was identified by the sources as the other high-ranking campaign official, received emails from Papadopoulos on multiple occasions but it is unclear if he responded. Lewandowski did not respond to questions from ABC News but told NBC’s ‘Today’ show that he didn’t know if he was one of the unnamed officials in the document.

“I was receiving thousands of emails a day,” he said. “You’re asking me to remember an email from April of 2016 when, on any given day, I would’ve received a thousand emails, and this would have come from a low-level volunteer.”

Clovis, however, the campaign’s national co-chairman who was identified as a campaign supervisor, responded directly to Papadopoulos, hailing him for his “great work” and saying “I would encourage you” to “make the trip, if it is feasible.”

Clovis currently serves as a senior White House adviser to the Department of Agriculture and has a Senate confirmation hearing for his nomination to be an Undersecretary at the Department of Agriculture next week.

An attorney for Clovis confirmed his role to ABC News, adding that he has not spoken to Papadopoulos since the 2016 election and any trip he would have taken would not have been authorized by the campaign and would have been done on his own personal time and money.