(Reuters) - The following is a timeline of significant developments in the investigation of Special Counsel Robert Mueller into U.S. intelligence agencies’ conclusions that Russia interfered in the 2016 presidential election to help get Donald Trump elected:

FILE PHOTO: Special Counsel Robert Mueller departs after briefing the U.S. House Intelligence Committee on his investigation of potential collusion between Russia and the Trump campaign on Capitol Hill in Washington, U.S., June 20, 2017. REUTERS/Aaron P. Bernstein/File Photo

2017

May 17 - U.S. Deputy Attorney General Rod Rosenstein appoints former FBI Director Mueller as a special counsel to investigate Russian meddling in the 2016 election and to look into any links and/or coordination between the Russian government and people associated with Republican Trump’s campaign.

The appointment follows President Trump’s firing of FBI Director James Comey on May 9 and days later Trump attributed the dismissal to “this Russia thing.”

June 15 - Mueller is investigating Trump for possible obstruction of justice, the Washington Post reports.

Oct. 30 - Veteran Republican political operative Paul Manafort, who was Trump’s campaign chairman for five months at crucial junctures in the run-up to the election, is indicted on charges of conspiracy against the United States and money laundering as is his business partner Rick Gates.

- Former Trump campaign adviser George Papadopoulos pleads guilty to a charge of lying to the FBI about his contacts with Russian officials.

Dec. 1 - Michael Flynn, Trump’s national security adviser for less than a month and who had a prominent campaign role, pleads guilty to the charge of lying to the FBI about his discussions in 2016 with the Russian ambassador to Washington.

2018

Feb. 16 - Federal grand jury indicts 13 Russians and three firms, including a Russian government propaganda arm called the Internet Research Agency, accusing them of tampering to support Trump and disparage Democratic candidate Hillary Clinton. The accused “had a strategic goal to sow discord in the U.S. political system, including the 2016 U.S. presidential election” according to the court document filed by Mueller.

- An American, Richard Pinedo, pleads guilty to identity fraud for selling bank account numbers after being accused by prosecutors of helping Russians launder money, buy Facebook ads and pay for campaign rally supplies. Pinedo was not associated with the Trump campaign.

Feb. 22 - Manafort and Gates charged with financial crimes, including bank fraud, in Virginia.

Feb. 23 - Gates pleads guilty to conspiracy against the United States and lying to investigators. He agrees to cooperate and testify against Manafort at trial.

April 3 - Alex van der Zwaan, the Dutch son-in-law of one of Russia’s richest men, is sentenced to 30 days in prison and fined $20,000 for lying to Mueller’s investigators, becoming the first person sentenced in the probe.

April 9 - FBI agents raid home, hotel room and office of Trump’s personal lawyer and self-described “fixer” Michael Cohen.

April 12 - Rosenstein tells Trump that he is not a target in Mueller’s probe.

April 19 - Former New York Mayor Rudy Giuliani, a Trump supporter in the election campaign, joins Trump’s personal legal team.

June 8 - Mueller charges a Russian-Ukrainian man, Konstantin Kilimnik, a Manafort business partner whom prosecutors suspect of having ties to Russian intelligence, with witness tampering.

July 13 - Federal grand jury indicts 12 Russians whom prosecutors describe as military intelligence officers, on charges of hacking Democratic Party computer networks in 2016 and staged releases of documents. Moscow, which denies interfering in the election, says there is no evidence that the 12 are linked to spying or hacking.

July 16 - In Helsinki after the first summit between Trump and Russian President Vladimir Putin, Trump publicly contradicts U.S. intelligence agencies, says no reason for Russia to meddle in election. He calls the Mueller inquiry a “rigged witch hunt” on Twitter.

Aug. 21 - A trial jury in Virginia finds Manafort guilty on eight counts of fraud.

- Cohen, in a case brought by U.S. prosecutors in New York, pleads guilty to tax fraud and campaign finance law violations. Cohen is subsequently interviewed by Mueller’s team.

Aug. 31 - Samuel Patten, an American business partner of Kilimnik, pleads guilty to unregistered lobbying for pro-Kremlin political party in Ukraine.

Sept. 14 - Manafort pleads guilty to some charges and signs a cooperation agreement with Mueller’s prosecutors.

Oct. 22 - Giuliani says Manafort’s lawyer has kept Trump informed about Manafort’s meetings with prosecutors and Manafort has not said anything damaging against the president.

Nov. 8 - U.S. Attorney General Jeff Sessions resigns at Trump’s request. He had recused himself from the Mueller inquiry because of his contacts with the Russian ambassador as a Trump campaign official; Trump appoints Sessions’ chief of staff Matthew Whitaker, a critic of the Mueller probe, as acting attorney general.

Nov. 20 - Giuliani says Trump submitted written answers to questions from Mueller.

Nov. 27-28 - Prosecutors say Manafort breached his plea deal by lying to investigators, which Manafort denies; Trump says he has not ruled out granting Manafort a presidential pardon.

Nov. 28 - Giuliani says Trump told investigators he was not aware ahead of time of a meeting in Trump Tower in New York between several campaign officials and Russians in June 2016.

Nov. 29 - Cohen pleads guilty in the Mueller investigation to lying to Congress about the length of discussions in 2016 on plans to build a Trump Tower in Moscow.

“I made these misstatements to be consistent with individual 1’s political messaging and out of loyalty to individual 1,” says Cohen, who previously identified “individual 1” as Trump.

- The president criticizes Cohen as a liar and “weak person.”

Dec. 12 - Two developments highlight growing political and legal risks for Trump: Cohen sentenced to three years in prison for crimes including orchestrating hush payments to women in violation of campaign laws before the election; American Media Inc, publisher of National Enquirer tabloid, strikes deal to avoid charges over its role in one of two hush payments. Publisher admits payment was aimed at influencing the 2016 election, contradicting Trump’s statements.

2019

Jan. 25 - Longtime Trump associate and self-proclaimed political “dirty trickster” Roger Stone charged and arrested at his home in Florida. Stone is accused of lying to Congress about statements suggesting he may have had advance knowledge of plans by Wikileaks to release hacked Democratic Party campaign emails.

Feb. 21 - U.S. judge tightens gag order on Stone, whose Instagram account posted a photo of the judge and the image of crosshairs next to it.

Feb. 22 - Manhattan district attorney’s office is pursuing New York state criminal charges against Manafort whether or not he receives a pardon from Trump on federal crimes, a person familiar with the matter says. Trump cannot issue pardons for state convictions.

Feb. 23 - Mueller’s office recommends no leniency in sentencing for Manafort for charges brought in federal court in Washington, describing him as a “hardened” criminal who repeatedly broke the law. Manafort, 69, is likely to spend the rest of his life in prison when he is sentenced in his Virginia case on March 7 with prosecutors recommending 19 -1/2 years to 24 -1/2 years.

Feb. 24 - Senior Democratic U.S. Representative Adam Schiff says Democrats will subpoena Mueller’s final report on his investigation if it is not given to Congress by the Department of Justice, and will sue the government and call on Mueller to testify to Congress if necessary.

Feb. 27 - Cohen tells U.S. House Oversight Committee Trump is a “racist,” a “conman” and a “cheat” who knew in advance about a release of emails by WikiLeaks in 2016 aimed at hurting rival Clinton. Trump directed negotiations for a real estate project in Moscow during the campaign even as he publicly said he had no business interests in Russia, Cohen testifies.

March 7 - Manafort was sentenced in the Virginia case to almost four years in prison. The judge also ordered Manafort to pay a fine of $50,000 and restitution of just over $24 million.