Jim Lo Scalzo/Pool Image via AP
President Donald Trump leaves after speech to a joint session of Congress on Capitol Hill in Washington, Tuesday, Feb. 28, 2017.
The charge has been denied by Obama, former Director of National Intelligence James Clapper, and, reportedly, FBI Director James Comey.
Sanders told "Good Morning America" anchor George Stephanopoulos that Trump does not accept Comey's denial, which has been reported by The New York Times and CNN.
"No I don't think he does, George," Sanders said, when asked pointedly if the president accepted the FBI director's denial.
Sanders, the deputy White House press secretary, also said on the "Today Show" that Trump "firmly believes" Obama ordered the alleged wiretaps on Trump Tower.
With no proof or evidence to back up his claim, Trump tweeted on Saturday morning that he "just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!"
White House counselor Kellyanne Conway also made a TV appearance Monday morning, speaking on "Fox and Friends," and was asked how Trump knew Obama tapped his phones.
"He's the President of the United States," Conway said. "He has information and intelligence that the rest of us do not."
Both Sanders' and Conway's statements came after White House Press Secretary Sean Spicer's statement Sunday that "Neither the White House nor the President will comment further" until the congressional intelligence committees investigate Trump's claims.