President Donald Trump's incendiary charge that predecessor Barack Obama tapped his phone during last year's election campaign has baffled political circles, elicited categorical denials from Obama-era officials and reportedly prompted Federal Bureau of Investigation director James Comey to ask the Department of Justice to publicly refute the allegation.
There has been no response so far from the Justice Department. A spokesman for Mr Trump said the President does not accept Mr Comey's refutation of the claims.
Mr Trump offered no evidence for the allegations, which seemed to stem from claims first broadcast by a conservative radio show host and then picked up by conservative website Breitbart, whose former chief executive, Mr Stephen Bannon, is now Mr Trump's top strategist.
A spokesman for Mr Obama denied that any wiretapping was ordered. Mr James Clapper, the Obama administration's director of national intelligence, also said the allegations were untrue.
"I can deny it," he told NBC on Sunday, when asked whether he could confirm or deny that a court order allowing for eavesdropping at Trump Tower in New York existed.
Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism!
Is it legal for a sitting President to be "wire tapping" a race for president prior to an election? Turned down by court earlier. A NEW LOW!
I'd bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!
How low has President Obama gone to tap my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!
General Michael Hayden, a former director of the Central Intelligence Agency and National Security Agency during the George W. Bush administration, said yesterday that the President cannot order such wiretapping and that, "to set the record straight", secret court records may need to be provided to Mr Trump in an "unprecedented" move, Bloomberg reported.
Mr Trump's allegations came after Attorney-General Jeff Sessions recused himself from investigations of Russian interference with the election, including probes into Russian contact related to the campaign with Mr Trump's associates.
That development put Mr Trump in a rage, US media reported, because it brought allegations of Russian links to his election campaign back into the spotlight.
Despite the lack of evidence, Mr Trump seemed adamant about the wiretapping.
Over the weekend, at his private estate in Florida, he reportedly told a friend, conservative media company Newsmax's chief executive Christopher Ruddy: "This will be investigated. It will all come out. I will be proven right." The Chicago Tribune quoted Mr Ruddy as saying: "I haven't seen him this angry."
Representative Devin Nunes, a Republican from California, said in a statement that the House Permanent Select Committee would look into Mr Trump's accusation as part of its larger investigation into Russian interference in the election.
What led to his outburst?
Previous US presidents have usually measured their words in public. So, Mr Donald Trump's bombshell tweets about his predecessor over the weekend have left many heads scratching. Pundits looking into what led to the outburst on Saturday have settled on at least three possibilities.
ANGER OVER JEFF SESSIONS REVELATION
Aides say that Mr Trump was furious last Friday over the news that Attorney-General Jeff Sessions had recused himself from any federal investigation into the Trump campaign's ties with Russia in response to reports that he had met Russia's ambassador during the presidential race.
Mr Trump was angry that Mr Sessions did not decide to fight "using the full defences of the White House", one colleague wrote. Mr Trump's anger spilt over into the weekend and fuelled his Twitter rage.
CHANGING THE SUBJECT
A Trump hallmark is making sensational claims often without regard for the full facts. Sometimes he does this to change the subject when he comes under too much scrutiny.
When it became clear that his election rival, Mrs Hillary Clinton, won the popular vote in the Nov 8 poll, he claimed voter fraud but provided no evidence to support the claim.
Facing severe criticism of his immigration policies, last Tuesday he claimed that the vast majority of individuals convicted for terrorism-related offences since 9/11 came from outside the US. Not true, says Homeland Security Department research, which says just over half the people Mr Trump talks about were born in the US.
LOVE OF CONSPIRACY THEORIES
Mr Trump has repeatedly supported conspiracy theories, particularly those involving former president Barack Obama. Mr Trump spent years promoting the false claim that Mr Obama was not born in the US. During the campaign last year, he asserted that Mr Obama was "the founder of ISIS (Islamic State in Iraq and Syria)".
So it seems unsurprising that he might leap on unsubstantiated reports in Breitbart Newsthat Mr Obama had used the "instrumentalities of the federal government" to wiretap the Republican seeking to succeed him.
NYTIMES, WASHINGTON POST
But Mr Trump's latest outburst has triggered widespread condemnation because it calls into question the highest office in the land. He also seemed to consult no one in his administration or the intelligence community before writing his series of tweets.
Representative Adam Schiff, a Democrat from California, said it was "clear that President Trump's claim that he was illegally wiretapped by President Obama was based on little more than Breitbart or other conspiracy-based news".
He added: "For a President of the United States to make such an incendiary charge - and one that discredits our democracy in the eyes of the world - is as destructive as it was baseless."
Several analysts have said that even if there was a wiretap authorised on a person in Mr Trump's establishment, it would have been authorised by a judge of the secretive Foreign Intelligence Surveillance Court.
But Senator Tom Cotton of Arkansas, a Republican on the Senate Intelligence Committee, said on Fox News Sunday he had not seen any evidence that the Obama administration wiretapped Trump Tower.