US President Donald Trump roundly criticised the FBI, insisting it acted "for no reason and with no proof" when it opened an investigation into whether he was acting on Russia's behalf after he fired the agency's director, James Comey, in May 2017.
The New York Times reported that the FBI launched the previously undisclosed counterintelligence investigation to determine whether Mr Trump posed a national security threat, at the same time that it opened a criminal probe into possible obstruction of justice by the president.
The FBI investigation was subsequently folded into the broader probe by Special Counsel Robert Mueller into Russia's meddling in the 2016 election and possible collaboration by the Trump campaign.
No evidence has publicly emerged that Mr Trump was secretly in contact with or took direction from Russian officials, the Times said.
"Wow, just learned in the Failing New York Times that the corrupt former leaders of the FBI, almost all fired or forced to leave the agency for some very bad reasons, opened up an investigation on me, for no reason & with no proof, after I fired Lyin' James Comey, a total sleaze!" Mr Trump tweeted.
According to Mr Trump, "the FBI was in complete turmoil... because of Comey's poor leadership" and the way he handled the investigation into Hillary Clinton's use of a private server to send some government emails.
"My firing of James Comey was a great day for America," Mr Trump said, describing the former FBI director as "a Crooked Cop who is being totally protected by his best friend, Bob Mueller."
Lyin’ James Comey, Andrew McCabe, Peter S and his lover, agent Lisa Page, & more, all disgraced and/or fired and caught in the act. These are just some of the losers that tried to do a number on your President. Part of the Witch Hunt. Remember the "insurance policy?" This is it!— Donald J. Trump (@realDonaldTrump) January 12, 2019
Asked in an interview with Fox News whether he had ever worked for Russia, Trump replied: "I think it's the most insulting thing I've ever been asked... I think it the most insulting article I've ever had written and if you read the article, you'd see that they found absolutely nothing."
Such standard reactions from Mr Trump "do nothing to address the incredibly serious nature of these allegations," said Democratic Congressman Jerrold Nadler, Chairman of the House Judiciary Committee.
"There is no reason to doubt the seriousness or professionalism of the FBI," Mr Nadler said in a statement which said his committee "will take steps to better understand both the president's actions and the FBI's response to that behavior, and to make certain that these career investigators are protected from President Trump's increasingly unhinged attacks."
The Times said that the FBI had been suspicious of Mr Trump's ties to Russia during the 2016 campaign.
But it held off on opening an investigation until the president sacked Mr Comey, who refused to pledge allegiance to Mr Trump and roll back the nascent Russia investigation.
Mr Trump has repeatedly criticised the Mueller probe as a "witch hunt" and views it as an attempt to besmirch the legitimacy of his presidency.
Secretary of State Mike Pompeo, who was CIA director at the time the investigation was launched, declined to comment on The New York Times report, but insisted in an interview with CBS that "the notion that President Trump is a threat to American national security is absolutely ludicrous."
Mr Mueller has indicted 33 people, including members of Russia's GRU military intelligence, and chalked up convictions against some of the president's close associates.
Mr Trump's ex-national security advisor, Michael Flynn, pleaded guilty to lying to investigators about his Moscow ties.
His former personal lawyer, Michael Cohen, has been sentenced to three years in prison for multiple crimes, including felony violations of campaign finance laws that prosecutors allege were carried out under Mr Trump's direction.
Mr Trump's former presidential campaign chairman, Paul Manafort, has been convicted in one case brought by Mr Mueller and pleaded guilty in another, over financial crimes related to his work in Ukraine before the 2016 campaign, and for witness tampering.
Mobile phone records show that Cohen was near Prague during the summer of 2016, supporting claims that he met there with Russian officials during the presidential election campaign, McClatchy news service has reported.
Cohen, who will testify in Congress on 7 February, insists that he has never been to Prague, but added in a tweet: "#Mueller knows everything!"
No emergency declaration to end US govt shutdown
President Trump has said he was holding off on declaring a state of emergency to end the partial US government shutdown that dragged into a 23rd day today, as he insisted on $5.7 billion to build a Mexico border wall that congressional Democrats oppose.
Asked by Fox News why he did not immediately declare a national emergency to secure the funds without congressional approval, Mr Trump said he wanted to give opposition Democratic lawmakers more time to strike a deal.
"I want to give them the chance to see if they can act responsibly."
The US government shutdown became the longest on record at midnight Friday, when it overtook a 21-day stretch in 1995-1996 under president Bill Clinton.
Mr Trump fired off a series of tweets yesterday in an effort to defend his stance and goad Democrats to return to Washington and end what he called "the massive humanitarian crisis at our Southern Border."
"Democrats could solve the Shutdown in 15 minutes!" he said in one tweet, adding in another, "We will be out for a long time unless the Democrats come back from their 'vacations' and get back to work. I am in the White House ready to sign!"
I just watched a Fake reporter from the Amazon Washington Post say the White House is "chaotic, there does not seem to be a strategy for this Shutdown. There is no plan." The Fakes always like talking Chaos, there is NONE. In fact, there’s almost nobody in the W.H. but me, and...— Donald J. Trump (@realDonaldTrump) January 12, 2019
We have a massive Humanitarian Crisis at our Southern Border. We will be out for a long time unless the Democrats come back from their "vacations" and get back to work. I am in the White House ready to sign!— Donald J. Trump (@realDonaldTrump) January 12, 2019
But most lawmakers left town on Friday and will not return before tomorrow, leaving little chance for any solution to the stalemate before then.
The impasse has paralysed Washington - its impact felt increasingly around the country - with the president refusing to sign off on budgets for swaths of government departments unrelated to the dispute.
As a result, 800,000 federal employees - including FBI agents, air traffic controllers and museum staff - received no pay cheques on Friday.