Earlier on Thursday, House Speaker Paul Ryan also said "no such wiretap existed".
"The intelligence committees, in their continuing, widening, ongoing investigations of all things Russia, got to the bottom - at least so far with respect to our intelligence community - that no such wiretap existed," Mr Ryan said at a news conference.
Republican chairman of the House intelligence committee Devin Nunes said on Wednesday he doesn't believe "there was an actual tap of Trump Tower".
But Mr Trump stood by his unverified allegations on Wednesday, telling Fox News a "wiretap covers a lot of different things".
He also hinted that more details about the alleged surveillance could be revealed in the coming weeks.
"Wiretap covers a lot of different things. I think you're going to find some very interesting items coming to the forefront over the next two weeks," he said in an interview broadcast on Wednesday night.
No evidence of wiretapping, according to:
former President Barack Obama
FBI Director James Comey
ex-Director of National Intelligence James Clapper
ex-CIA Director John Brennan
Republican chairman of House intelligence committee, Devin Nunes
Republican John McCain, who chairs Senate Committee on Armed Services
House Speaker Paul Ryan
Former White House Chief of Staff Denis McDonough
Mr Trump echoed comments from White House Press Secretary Sean Spicer, who said the president used the word "wiretap" in quotes to broadly refer to "surveillance and other activities".
The White House has yet to provide any evidence of the president's claims, and instead has asked Congress to examine the allegation as part of a wider investigation into alleged Russian interference in last year's election.
Not news to any rational person who can see through Trump's gaslighting, I suppose.