Mr Trump last weekend accused Mr Obama of electronically eavesdropping on him shortly before the November election. He did so without providing any evidence, and the White House called on Congress to investigate the claim.
White House press secretary Sean Spicer insisted Mr Trump still believed the allegation he had made. Yet he said the President had used the word “wiretap” to more broadly refer to surveillance or other activities.
“He does not think Obama went out there and wiretapped him personally,” he said. “There are are a whole host of techniques to or surveil someone.”
Made in a series of early morning tweets on 4 March, Mr Trump’s accusation was not only startling, but very specific.
“Terrible! Just found out that Obama had my “wires tapped” in Trump Tower just before the victory. Nothing found. This is McCarthyism,” he wrote.
He added: “How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy.”
Mr Obama denied through a spokesman that he had ever ordered such actions. The White House, scrambling to provide evidence to back up the President’s claims, said Mr Trump had based his accusation on media reports, including the right-wing Breitbart News.
The House and Senate Intelligence Committees agreed to take up Mr Trump’s accusation as part of a probe already underway into Russia’s alleged interference into the 2016 election. The White House has said it expects the Department of Justice to comply with a request to provide politicians on Capitol Hill with any supporting evidence by Monday.
It said it will not comment further until Congress has investigated and reported back.
But Mr Trump has been under pressure to explain why he made the claim, and whether he had any evidence to substantiate. Over the weekend, senior Republican senator John McCain, said the president should either prove the claim or retract it.
“I have no reason to believe that the charge is true, but I also believe that the President of the United States could clear this up in a minute,” Mr McCain told NBC.
“All he has to do is pick up the phone, call the director of the CIA, director of national intelligence and say, ‘OK, what happened’.”
He added: “The president has one of two choices, either retract or provide the information that the American people deserve.”
On Monday morning, Mr Trump’s communications advisor, Kellyanne Conway, brushed off Mr McCain’s demands.
“We will comment further after those findings are made clear,” she said.
In an interview with USA Today, she suggested Mr Trump may have been spied on by use of a microwave.
“What I can say is there are many ways to surveil each other. You can surveil someone through their phones, certainly through their television sets – any number of different ways,” she said.
“Surveillance could be conducted with microwaves that turn into cameras. We know this is a fact of modern life.”