Former FBI Director James Comey will testify to the US Senate Intelligence Committee on Thursday about Russian involvement in the 2016 presidential election.
President Donald Trump's abrupt firing of Comey on May 9 renewed attention to allegations by US intelligence agencies that Russia interfered in the election to benefit Trump. It also raised questions about the motivations behind Comey's dismissal.
The following describes what is publicly known and not known about US investigations into meddling and possible collusion between Russia and members of the Trump campaign:
How did the investigations begin?
Former President Barack Obama ordered US intelligence agencies to assess whether Russia tried to intervene in the election after a cyber attack 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 Nov. 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 ordered a campaign not just to undermine confidence in the US electoral system but 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 sway public opinion, the agencies said.
The report stopped short of assessing whether Russia succeeded in swaying the election result.
Putin and other Russian officials have repeatedly denied interfering in the US election.
How many US probes are there into Russia's election meddling?
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.
The Justice Department announced on May 17 that it has appointed Robert Mueller, a former FBI director, as special counsel to lead an independent Russia probe. Mueller would, if the evidence merits, work in tandem with the FBI to handle any related criminal prosecutions.
In addition there are multiple committees in the Senate and House of Representatives investigating various aspects of Russian election meddling.
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 an 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 US 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 Jan. 11 news conference ahead of his inauguration. "As far as hacking, I think it was Russia," Trump said, although he added: "It could have been others also."
Trump said in May that China may have hacked the emails of Democratic officials to meddle with the election, offering no evidence and countering the view of intelligence officials.
Trump has made clear on multiple occasions he believes 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 May 8.
On May 30, Trump wrote on Twitter: "Russian officials must be laughing at the US & how a lame excuse for why the Dems lost the election has taken over the Fake News."