As the probe into Russia’s influence in the 2016 presidential election continues, Special Counsel Robert Mueller’s investigation has led to one of its most significant charges to date.
Michael Flynn, Trump's former national security adviser, was charged on Dec. 1 for lying to the FBI about his communications with a Russian ambassador.
Paul Manafort, 68, the former campaign chairman for President Trump, and his associate, Rick Gates, 45, were indicted by a federal grand jury in October for charges stemming from conspiracy against the U.S., to conspiracy to launder money.
George Papadopoulos, 30, who served as a foreign policy adviser on Trump's presidential campaign, pleaded guilty on Oct. 5 to making false statements to FBI agents, according to unsealed court documents.
Additionally, Mueller removed FBI agent Peter Strzok from the case over potential anti-Trump text messages, Peter Carr, the spokersperson for the special counsel, told Fox News.
Mueller, 73, impaneled a grand jury earlier in August as part of his examination.
The Department of Justice announced the appointment of Mueller to oversee the federal investigation into Russia’s alleged meddling in the 2016 election on May 17.
The appointment came after a growing cry – mostly from Democrats – mounted for someone outside the Justice Department to handle the probe. Attorney General Jeff Sessions had already recused himself from the investigation.
Mueller led the FBI through the Sept. 11 terrorist attacks and served under presidential administrations of both parties.
He has the authority to prosecute any crimes uncovered during his investigation, and he was given wide authority to investigate whether Trump or his associates colluded with the Kremlin to win the White House.
Mueller allegedly expanded the probe to include investigating Trump for obstruction of justice because he fired FBI Director James Comey earlier in May.
Trump told Fox News the claims that he obstructed justice were "ridiculous" and said Mueller's friendship with Comey was "very bothersome."
The Trump administration heavily criticized Mueller’s investigation as several of his attorneys on staff donated to Democratic campaigns, including to Trump’s 2016 rival, Hillary Clinton.
“They clearly wanted the other person to win. Now, whether that prejudices them in one way or another remains to be seen, but it is relevant information for people to have,” White House counselor Kellyanne Conway told "Fox and Friends" in July.
Mueller kicked off August by impaneling a grand jury to investigate Russia’s influence – an indication that the probe was entering a new phase.
A grand jury gives prosecutors the ability to subpoena documents and gather on-the-record witness testimonies. Indictments can also be sought.
Grand juries are common vehicles to gather evidence, though they do not suggest any criminal charges are near or will necessarily be sought.
Speaking to reporters on the South Lawn at the White House on Dec. 2, Trump once again dismissed the allegations of collusion with Russia.
"No collusion – absolutely no collusion," he said. "We'll see what happens [with Flynn]."
Trump added that he was not worried about what Flynn will say to the special counsel.
"I just hope the final determination is a truly honest one..."
Previously, Trump dismissed the allegations of collusion with Russia as a “fake story that is demeaning to all of us and most of all demeaning to our country and demeaning to our Constitution.”
"I just hope the final determination is a truly honest one, which is what the millions of people who gave us our big win in November deserve and what all Americans who want a better future want and deserve," Trump said at a rally in West Virginia earlier this year.
The president also warned Mueller to stay within certain boundaries as he investigates.
But Conway told Fox News that the Trump administration is not “discussing” firing Mueller and will cooperate with the investigation.
Trump and Mueller have also sent messages “back and forth,” according to Trump’s outside counsel. A spokesman for Mueller told Fox News that the messages have been “very professional.”
Mueller also took over an ongoing investigation into Manafort's financial dealings in Ukraine. The FBI executed a search warrant earlier this year at the Virginia home of Manafort, who – prior to joining Trump’s campaign – worked with a Russia-backed Ukrainian president.
Manafort and Gates were indicted on Oct. 27 that contains 12 counts: conspiracy against the U.S., conspiracy to launder money, unregistered agent of a foreign principal, false and misleading [Foreign Agents Registration Act] statements, false statements, and seven counts of failure to file reports of foreign bank and financial accounts, a spokesperson for the Special Counsel's Office told Fox News.
In a tweet, Trump said the allegations against Manafort were prior to him joining the campaign and alleged that Clinton should be the focus of Mueller's probe.
"Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus?????" Trump tweeted.
Flynn was charged in December for lying to the FBI about certain conversations he had with a Russian ambassador. He pleaded guilty.
Papadopoulos pleaded guilty to one count of making false statements to investigating FBI agents, according to court documents.
Tony Podesta, the brother of Hillary Clinton’s campaign chairman, and his lobbying firm are also now a subject in Mueller’s investigations because of the firm’s involvement with Manafort’s PR campaign for a pro-Ukraine group.
The Podesta Group has maintained that it’s been in compliance with regulations and is cooperating with the Special Counsel’s Office.
The Associated Press contributed to this report.