(Reuters) - Michael Flynn, a former campaign adviser to U.S. President Donald Trump who also served briefly as his national security adviser, was slated to be sentenced in court on Tuesday.

FILE PHOTO: Michael Cohen, U.S. President Donald Trump's former lawyer, arrives for his sentencing at United States Court house in the Manhattan borough of New York City, New York, U.S., December 12, 2018. REUTERS/Jeenah Moon/File Photo

The retired U.S. Army general is one of dozens of people who have been caught up in a long-running investigation of Russian meddling in the 2016 U.S. presidential election and possible collusion between the Kremlin and the Trump campaign.

Trump denies any collusion and has long denounced the probe being led by Special Counsel Robert Mueller as a “witch hunt.” Moscow has denied it interfered in the election.

Here are some others who have pleaded guilty, been indicted or otherwise been swept up in the inquiry, which has clouded Trump’s presidency and has recently intensified.

MICHAEL FLYNN

Flynn pleaded guilty in December 2017 to lying to the FBI about his contacts with Russia during Trump’s presidential transition and agreed to cooperate with Mueller.

He was Trump’s national security adviser for less than a month in early 2017. He resigned after it emerged he had misled Vice President Mike Pence and the FBI about his dealings with the then-Russian ambassador to the United States, Sergey Kislyak.

Flynn knew better than to lie to the FBI and does not deserve sentencing leniency, U.S. prosecutors said on Friday. He is scheduled to be sentenced on Tuesday.

MICHAEL COHEN

Trump’s former personal lawyer Cohen was sentenced last week to three years in prison for crimes including orchestrating hush-money payments to women in violation of campaign laws before the 2016 election, and he promised to keep cooperating with the U.S. government against his former boss.

Trump directed the hush payments to the two women shortly before the election and knew that doing so was wrong, Cohen said in a television interview aired on Friday.

Cohen pleaded guilty on Nov. 29 to lying to Congress about a Trump Organization skyscraper project in Moscow.

Cohen once said he would “take a bullet” for Trump, who called him a “Rat” in a tweet on Sunday.

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PAUL MANAFORT

Trump’s former campaign chairman, Manafort agreed to cooperate with Mueller in a plea deal announced in September. U.S. prosecutors on Nov. 26 accused him of breaching his deal by lying to investigators.

Manafort in September pleaded guilty to conspiracy against the United States and agreed to cooperate with Mueller.

He was convicted in August in a separate case in Virginia of bank and tax fraud.

RICK GATES

A former deputy Trump campaign chairman, Gates pleaded guilty in February 2018 to conspiracy against the United States and lying to investigators. He agreed to cooperate with Mueller and he testified against Manafort, his former business partner.

KONSTANTIN KILIMNIK

A Manafort aide in Ukraine and a political operative with alleged ties to Russian intelligence, Kilimnik was charged in June with tampering with witnesses about their past lobbying for Ukraine’s former pro-Russian government.

GEORGE PAPADOPOULOS

A former Trump campaign adviser, Papadopoulos was sentenced in September to 14 days in prison after pleading guilty in October 2017 to lying to the FBI about his contacts with Russian officials, including a professor who told him the Russians had “dirt” on Trump’s Democratic presidential rival Hillary Clinton.

SAMUEL PATTEN

An American business partner of a Russian national accused by Mueller’s office of ties to Russian intelligence, Patten pleaded guilty in August 2018 to unregistered lobbying for a pro-Kremlin political party in Ukraine. He agreed to cooperate with investigators.

RICHARD PINEDO

Pinedo was not involved with the Trump campaign, but in February he pleaded guilty to identity fraud in a case related to the Mueller probe for helping Russian conspirators launder money, purchase Facebook ads and pay for supplies.

He was sentenced in October 2018 to a year of incarceration and allowed to serve half of it at home.

RUSSIAN OFFICERS

Twelve Russian intelligence officers were indicted by a federal grand jury on July 13, accused of hacking Democratic Party computer networks in 2016.

RUSSIAN NATIONALS, ENTITIES

Thirteen Russians and three Russian entities were indicted in Mueller’s investigation in February 2018, accused of tampering in the 2016 election to support Trump.

ALEX VAN DER ZWAAN

A lawyer who once worked closely with Manafort and Gates, Van der Zwaan pleaded guilty in February to lying to Mueller’s investigators about contacts with a Trump campaign official. He was sentenced in April to 30 days in prison and fined $20,000.