Mr Trump made his latest explosive claims on Twitter without offering supporting evidence, saying he was the target of a Watergate-style plot and his New York office was wiretapped during the election campaign against Hillary Clinton.
Two former senior US officials dismissed Mr Trump's accusations out of hand as “just nonsense” and “just wrong”, with one telling CNN categorically: “This did not happen”.
Mr Trump, who has frequently railed against “fake news”, apparently relied on conservative media sources rather than intelligence briefings to support his allegations – to the exasperation of members of his own team.
One White House official is reported to have “grimaced” when he woke up and saw the President’s fluffy of tweets, according to Politico.
“It could have come from anywhere”, the official reportedly said, adding it was unlikely to have been an official source.
“Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower before the victory. Nothing found. This is McCarthyism!” the President tweeted, in a reference to Cold-war era allegations of espionage without evidence.
Breitbart, the right-wing media outlet previously run by Mr Trump’s chief strategist Steve Bannon, published a story accusing the Obama administration of having monitored Trump Towers during the election campaign.
The Breitbart story, which claimed the tactics were designed to undermine Mr Trump’s bid for the White House in a similar way to the “Plumbers” plot against the Democrats by President Nixon, referenced commentary by radio host Mark Levin.
But neither Breitbart nor Mr Levin offered any independent reporting or cited any intelligence sources to support their allegations.
“A cardinal rule of the Obama administration was that no White House official ever interfered with any independent investigation led by the Department of Justice,” Kevin Lewis, a spokesman for Mr Obama, said in a statement on Saturday, which did not deny there had been wire-tapping of Trump Towers but did deny the former President had authorised it.
“As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any US citizen. Any suggestion otherwise is simply false.”
Ben Rhodes, Obama’s former deputy national security adviser, also denied Mr Trump’s claims.
“No President can order a wiretap,” Mr Rhodes said on Twitter in a direct response to Mr Trump. “Those restrictions were put in place to protect citizens from people like you.”
Conservative radio host Mr Levin, a former aide to President Reagan, used his show to discuss stories in the New York Times and other outlets that the Obama administration had put the Trump campaign under surveillance to see if there were any links to Russian banks.
“The question is: Was Obama surveilling top Trump campaign officials during the election?” Mr Levin asked.
“We absolutely know this is true,” he claimed, comparing the alleged tactics to those of a “police state”.
Breitbart’s report referenced Levin’s claims and outlined other news stories, dating back to June 2016, about alleged actions taken against Mr Trump by intelligence agencies rather than by Mr Obama.
Although media commentators have repeatedly speculated on whether Mr Trump will be impeached, the President drew his own comparison between Mr Obama and disgraced former President Nixon, who was forced to resign in the wake of the Watergate scandal where the Democratic headquarters were monitored illegally in the lead-up to the 1972 election.
“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!” Mr Trump said in a tweet.
“How low has President Obama gone to tapp (sic) my phones during a very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!”
The tweets were issued two days after Attorney General Jeff Sessions said he would excuse himself from any investigations into possible ties between the Trump campaign and the Russian Government.
Mr Trump’s flurry of Tweets prompted several members of Congress to call on the President to be more specific about the allegations.
Senator Ben Sasse, a Nebraska Republican and Trump critic, said the allegations suggest that even if Mr Obama wasn’t involved, a court may have seen sufficient evidence to authorise a wiretap.
Legal wiretapping could have been initiated by intelligence agencies, with court approval required under the Foreign Intelligence Surveillance Act.
Under US law, a FISA court approving a wiretap of Mr Trump’s home or offices would have had to find probable cause that the facility was being used on behalf of a foreign power, or that Mr Trump’s associates were involved in espionage.
Such a wiretap could have been obtained without Mr Obama’s involvement, if intelligence agencies determined — and got a court to agree — that Mr Trump or his associates were acting on behalf of a foreign government.
Mr Trump has repeatedly denied colluding with Russia, saying he has no links to the country and that all such suggestions are “fake news” put about by the mainstream media.
The New York Times reported last year that the FBI was investigating Russia’s possible links to the US elections campaign and said agents had scrutinised advisers close to Mr Trump for any connections to Russian financial figures.
Mr Trump suggested he could take legal action over the alleged phone-tapping.
“I’d bet a good lawyer could make a great case out of the fact that President Obama was taping my phones in October, just prior to the election.”
House Democratic Leader Nancy Pelosi mocked Mr Trump’s claims on Twitter: “The Deflector-in-Chief is at it again. An investigation by an independent commission is the only answer.”
After setting social media alight with his allegations, Mr Trump went to play a round of golf at his Mar-a-Lago resort in Florida before returning to Twitter to attack Arnold Schwarzenegger for his ratings on The Apprentice, which the President used to host.Reuse content