President Donald Trump's firing of FBI Director James Comey on Tuesday renewed attention to allegations by U.S. intelligence agencies that Russia interfered in the 2016 election campaign to benefit Trump.
The following describes what is publicly known and not known about U.S. investigations into meddling by the Russians, and possible collusion between Russia and members of the Trump campaign:
How did the investigations begin?
Former President Barack Obama ordered U.S. intelligence agencies to assess whether Russia tried to intervene in the election after a cyberattack on the Democratic National Committee in July 2016 and the publication of thousands of hacked personal emails from Hillary Clinton's campaign manager in the month before the November 8 election. Obama told intelligence officials to deliver a report on possible foreign interference before he left the White House in January 2017.
What did the intelligence agencies find?
The Central Intelligence Agency, the Federal Bureau of Investigation and the National Security Agency concluded in a report declassified in January that Russian President Vladimir Putin had ordered a campaign not just to undermine confidence in the U.S. electoral system but to try to affect the outcome.
The agencies said Putin and the Russian government had a "clear preference" for Trump to win the White House. Putin's associates hacked information, paid social media "trolls" and backed efforts by Russian government agencies and state-funded media to try to sway public opinion, the agencies said.
The report stopped short of assessing whether Russia had succeeded in swaying the election result.
Putin and other Russian officials have repeatedly denied interfering in the U.S. election.
What has Trump said about Russia's role in the election?
Trump has not taken a clear public position.
"I will tell you this, Russia: if you're listening, I hope you're able to find the 30,000 emails that are missing," Trump said at a July 2016 news conference, in reference to a FBI probe into Clinton's use of a private email system when she was secretary of state and emails that had possibly been deleted.
Trump subsequently dismissed reports, including from U.S. intelligence officials, that Russia had attempted to intervene in the election on his behalf.
The first time Trump said he accepted the findings of the intelligence agencies was at a January 11 news conference ahead of his inauguration. "As far as hacking, I think it was Russia," Trump said, although he then added: "It could have been others also."
Earlier this month, Trump said China may have hacked the emails of Democratic officials to meddle with the election, offering no evidence and countering the view of intelligence officials.
How many U.S. probes are there into Russia's election meddling?
Committees in the House of Representatives and the Senate, along with the U.S. Department of Justice and the Federal Bureau of Investigation, are all known to be investigating. Some Democrats and Trump critics have also called on the Justice Department to appoint a special counsel.
Has there been any fallout for Trump associates over contacts with Russia before, during or after the election campaign?
Michael Flynn, Trump's national security adviser, was fired in February. The White House said he had misled Vice President Mike Pence about the contacts he'd had with Russia's ambassador to the United States, Sergei Kislyak, before Trump took office.
On Tuesday, federal prosecutors issued grand jury subpoenas seeking business records from people who worked with Flynn when he was a private citizen.
On Wednesday, the Senate Intelligence Committee issued the first subpoena in its Russia investigation, demanding documents from Flynn after he declined to voluntarily comply with an earlier request.
Attorney General Jeff Sessions had to recuse himself from involvement in Russia-related probes at the Justice Department because he had not told Congress of his own contacts with Kislyak in 2016.
Will the FBI probe continue after Comey's dismissal?
Comey told the House Intelligence Committee on March 20 that the FBI was investigating Moscow's role in the election, including possible collusion with Trump's campaign. It was the first time he publicly acknowledged the agency was investigating the matter.
Comey's departure does not necessarily mean the FBI's Russia investigation will be disrupted or ended, because the career FBI officials Comey put in charge of it will most likely continue working on the matter even as the search for a new director begins.
The leaders of the Senate Intelligence Committee had raised concerns about the pace of the FBI inquiry before Comey's firing. The congressional probes are dependent on the intelligence produced by the FBI and other agencies.
FBI acting Director Andrew McCabe, who will lead the agency until a new director is hired, promised the Senate Intelligence Committee that Comey's firing would not affect the investigation and that he would notify the committee of any attempt to delay or derail it.
Why was Comey fired?
Sessions sent Trump a letter Tuesday attaching a memo from Deputy Attorney General Rod Rosenstein on "Restoring Confidence in the FBI" that recommended Comey's dismissal.
Rosenstein's memo said Comey erred in July 2016 by announcing the FBI had been examining Clinton's use of a private email server and that the case should be closed without prosecution. Rosenstein's view was that Comey's decision to make a public statement on the matter broke with long-standing FBI precedent and should have been handled by the then-U.S. Attorney General Loretta Lynch.
Trump called Comey a "showboat" and "grandstander" in an interview with NBC News on Thursday, saying he was going to fire Comey regardless of Rosenstein's recommendation.
Did Comey's firing have anything to do with the Russia probe?
The White House says Comey was dismissed because of his handling of the Clinton email investigation. But many Democrats challenged that, and some Republicans have expressed skepticism, given the delay between Trump's taking office on January 20 and Comey's dismissal.
Trump aides have told Reuters that top Justice Department officials wanted a heads-up from Comey about what he would say during a May 3 congressional hearing about the FBI's investigation of Clinton's private email system.
The hearing came just days after Clinton said at a New York event that announcements by Comey in October 2016, a week before the election, that he had reopened and then reclosed the email probe had swung the election for Trump. Comey told the congressional panel the idea that he might have affected the election result made him "mildly nauseous."
Just days before his firing, Comey asked Rosenstein for a significant boost in resources to fund the agency's Russia probe, according to media reports. The Justice Department has denied this request was made.
Is Trump being investigated by the FBI?
In the short letter Trump sent to Comey dismissing him from the FBI, he thanked Comey for informing him three times that he was not under investigation. Comey has never stated publicly whether the FBI was investigating Trump, and it would be unorthodox for him to say such a thing to the president. The White House has offered no proof to back up Trump's claim.
Trump has made clear several times that he thinks the Russia investigations have run their course and should be closed. "The Russia-Trump collusion story is a total hoax, when will this taxpayer funded charade end?" he wrote on Twitter on Monday.