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WASHINGTON (KDKA/AP) – President Donald Trump’s former campaign chairman, Paul Manafort, and a former business associate, Rick Gates, have surrendered to authorities.

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Those are the first charges in special counsel Robert Mueller’s investigation into potential coordination between Russia and the Trump campaign. The New York Times on Monday cited an anonymous person involved in the case.

According to CBS News, Manafort surrendered at FBI headquarters Monday morning. He was accompanied by his lawyer.

Manafort and Gates have pleaded not guilty following their arrest on charges related to conspiracy against the United States and other felonies.

Manafort and Gates appeared before a federal judge Monday in Washington. They are charged with a combined 12 counts, including conspiracy to launder money, unregistered agent of a foreign principal, false and misleading FARA statements, false statements, and seven counts of failure to file reports of foreign bank and financial accounts.

The top Democrat in the House is pressing for an “outside, fully independent investigation” to expose Russia’s meddling in the election and the involvement of Trump officials.

That’s the word from Minority Leader Nancy Pelosi of California. In a statement Monday shortly after indictments were unsealed, Pelosi said that even with the accelerating special counsel probe and congressional investigations, another inquiry was warranted.

Pelosi said that defending the integrity of the country’s democracy “demands that Congress look forward to counter Russian aggression and prevent future meddling with our elections.”

Mueller was appointed as special counsel in May to lead the Justice Department’s investigation into whether the Kremlin worked with associates of the Trump campaign to tip the 2016 presidential election.

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The White House initially declined comment on the situation. However, Trump has taken to Twitter to say the alleged misdeeds by Manafort were “years ago.”

Additionally, a former campaign aide to President Donald Trump has pleaded guilty to lying to federal agents working for special counsel Robert Mueller as part of his probe into possible coordination between the Trump campaign and Russia.

George Papadopoulos pleaded guilty on Oct. 5 to one count of lying to FBI agents about the nature of his interactions with “foreign nationals” who he thought had close connections to senior Russian government officials. The plea was unsealed Monday.

Papadopoulos is the first person to face criminal charges that cite interactions between Trump campaign associates and Russian intermediaries during the 2016 presidential campaign.

Papadopoulos was a member of the campaign’s foreign policy team. But Trump aides have said he played a limited role in the campaign and no access to Trump.

Meanwhile, Trump’s campaign is telling supporters that he is “still standing” after Manafort and Gates turned themselves in to authorities.

The fundraising e-mail from Eric Trump, the president’s son, warns that “There’s new opposition against my father and this Administration every day” and asked supporters to contribute to the re-election effort. The message adds: “as a loyal support of our movement, I know you know the truth.”

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(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)