After months of speculation about the investigation overseen by special counsel Robert Mueller, charges were filed Monday against Paul Manafort and Rick Gates.

Multiple congressional committees and Mueller's team of prosecutors are investigating whether the Donald Trump election campaign co-ordinated with Russia to influence the outcome of the 2016 election.

Campaign foreign policy adviser George Papadopoulos, described by Trump in 2016 as an "excellent guy," has been convicted for lying to the FBI in its investigation, court documents indicated on Monday.

How far along Mueller's investigation is remains unclear. He is free to pursue charges with respect to any criminal activity uncovered during the course of the investigation.

Here are some names to know at this juncture in the storyline.

Sam Clovis

Iowa Senate GOP Primary-Sam Clovis

(Charlie Neibergall/Associated Press)

Clovis, a nominee for an advisory position at the U.S. Department of Agriculture, served as co-campaign chair for Trump.

According to a Washington Post report on Monday night, Clovis is the unnamed senior official in the newly released court documents who allegedly said in an August 2016, "Make the trip, if it is feasible," in response to Papadopoulos's offer to meet with Russian officials.

A spokesperson for Clovis said it was understood that any trip Papadopoulos undertook would be in "a personal capacity."

Michael Flynn

USA-TRUMP/RUSSIA/MICHAEL FLYNN

(Carlos Barria/Reuters)

During the transition from campaign to administration, Flynn did not reveal that he received money for a speech in Russia in 2015, and the White House said it was unaware he received $530,000 in exchange for lobbying last year on behalf of a Turkish businessman and ally of president Tayyip Erdogan.

More recently, it was revealed he served as an adviser for Cambridge Analytica, the data mining company funded by right-wing financier Robert Mercer that has come under scrutiny.

Trump chose Flynn as national security adviser but acting attorney general Sally Yates later testified that she quickly sounded the alarm because Flynn "essentially could be blackmailed" since he had lied to Vice-President Mike Pence and others over contacts with Sergei Kislyak, then Russian ambassador to the U.S.

Flynn was let go a month into the job. After Flynn was gone, Trump pressed the FBI to back away from any investigation into Flynn, according to testimony from former agency director James Comey. Trump denies that charge.

Rick Gates

Trump Russia Probe-Rick Gates

(Evan Vucci/Associated Press)

Gates, 45, has a professional relationship stretching back two decades with Manafort, and served as Trump's deputy campaign chair during the period Manafort was campaign chair.

Prosecutors allege the Chicago native and Manafort worked for several years as unregistered agents of the government of Ukraine and the Party of Regions, a pro-Russian political party led by Victor Yanukovych. 

Gates was indicted on eight counts involving fraud and conspiracy against the U.S. and could face up to 70 years in prison.

The indictment says that up to $75 million flowed from their activities through overseas accounts they controlled. Gates is alleged to have transferred more than $3 million to accounts he controlled.

The Trump administration has asserted that the Manafort-Gates charges predate the election campaign and had nothing to do it, though they do raise the issue of the apparent lack of vetting of campaign officials.

Jared Kushner

US Mideast-Kushner

(Pablo Martinez Monsivais/Associated Press)

The president's son-in-law, Kushner attended a June 2016 meeting at Trump Tower with a Russian lawyer. Accounts vary on what the purpose of the meeting was.

During president-elect Trump's transition, Kushner reportedly suggested using Russian diplomatic facilities and equipment for back-channel communications between officials of the two countries, which some experts said at minimum illustrated extreme naiveté.

In one of his few public comments, Kushner, now a key White House adviser, said he did not collude with Russia and knew no one on the campaign who did. The wealthy husband of Ivanka Trump also said he wasn't beholden to Russian money in his business pursuits.

Paul Manafort

Trump Russia Probe-Manafort

(Alex Brandon/Associated Press)

The indictment of Manafort was not a complete surprise, as his Virginia home had been searched,

Manafort has been indicted on nine counts involving fraud and conspiracy and could face up to 80 years in prison.

Now under house arrest, he is accused of laundering money through scores of U.S. and foreign entities to hide payments from U.S. authorities to the tune of $18 million, apparently enjoying a lavish lifestyle with his wealth.

The allegations cover a period of several years, raising the question for many of why Manafort would get involved in a presidential campaign and potentially subject his dealings with pro-Russia factions in Ukraine to scrutiny.

Carter Page

USA-TRUMP/RUSSIA/CARTER PAGE

(Sergei Karpukhin/Reuters)

Page, a former Merrill Lynch investment banker who worked out of its Moscow office for three years, has gained media attention in the saga for being remarkably up front in interviews about his time with the Trump campaign. As well, he has answered questions at the related congressional inquiries without a lawyer present.

Page said Monday night in an interview with MSNBC that the subject of Russia "may have come up" in email chains he and Papadapolous were a party to, but that it was just a small part of email traffic during a busy campaign.

Page has previously admitted to meeting with Kislyak during last year's Republican convention, and it is alleged in the infamous dossier that found its way into the hands of Trump campaign rivals on both the right and the left that he also met with at least two other Russians with connections to the Kremlin.

Now an energy industry consultant, Page has said he's confident the Mueller probe will find no evidence of collusion.

George Papadopoulos

Papadopoulos

George Papadopoulos is seen on the far left on March 31, 2016. (Donald Trump/Instagram)

Papadopoulos was publicly introduced as a Trump foreign policy adviser in late March 2016. Soon, he took a meeting in London with a professor and a woman who he was led to believe was a niece of president Vladimir Putin. He reported to Trump and other senior officials on March 31 that he had connections that could help arrange a meeting between then-candidate Trump and President Putin.

"The Russians had emails of Clinton," Papadopoulos was then told by the professor during a meeting in April. Papadopoulos soon emailed a Trump campaign policy adviser: "Have some interesting messages coming in from Moscow about a trip when the time is right."

The stealing of emails and documents from the Democratic National Committee became public in July 2016. U.S. intelligence has concluded that Russia was behind the intrusion.

Papadopoulos was arrested in July of this year and has been co-operating with investigators, it has been learned.

Trump and the White House have distanced themselves, branding Papadopoulos a low-level campaign volunteer and a liar.

Jeff Sessions

Opioid Crisis Sessions

(Mark Lennihan/Associated Press)

Sessions, among others, was in the March 31, 2016 meeting in which Papadopoulos talked about making Russian connections.

The attorney general can ill-afford any more missteps. He has managed to anger many on the left who believe he knowingly lied in confirmation hearing testimony over his contacts with Russia, as well as those on the right, for recusing himself from any inquiries into Russian collusion.

The latter decision helped pave the way for the appointment of ex-FBI director Mueller as special counsel. The critics of his recusal include the president, who went so far as to publicly lament hiring Sessions.

Sessions has said any of his dealings with Russia were in his role as senator and not related to his involvement with the campaign, his denials in Senate testimony angry in nature.

Donald Trump Jr.

Donald Trump Jr.

(Richard Drew/Associated Press)

Trump Jr. released an email chain in mid-July in which he discussed plans to hear damaging Clinton information.

"If it's what you say I love it especially later in the summer," Trump Jr. replied to an intermediary working to connect Trump repesentatives to a Russian attorney. That attorney, Natalia Veselnitskaya, has denied that she ever represented having any Clinton dirt or that she has any connections to Putin.

The president's son has said the June 9, 2016 meeting at Trump Tower was ultimately short and unproductive and that, "in retrospect, I probably would have done things a little differently."

He did admit he went for the purposes of "opposition research."

Donald Trump

Governors Race Trump

(Alex Brandon/Associated Press)

Trump, facing daily Gallup poll approval ratings as low as 33 per cent, according to the Washington Post, has made at least three previous statements that could come back to haunt him. They include encouraging Russia to unearth Clinton emails not long after the DNC hack became public, the private meeting with Comey in which he may have leaned on the FBI director to end inquiries into Flynn, and an NBC interview on May 11 in which he said he fired Comey because of "this Russia thing," contradicting the initial stated reasoning of firing the FBI director over his handling of the investigation into Clinton's use of a homebrew email server when she was Secretary of State.

Democrats have repeatedly raised the fear that Trump will find a way to fire Mueller, but the White House as recently as Monday said the president wasn't considering that.

With files from Associated Press and Reuters