Transcript for Presenting no evidence, Trump accuses Obama of spying on him
We begin tonight with that breaking news, president trump's striking allegations against former president Barack Obama. President trump in a Twitter tirade accusing the former president of spying on him at trump tower by wiretapping phones but offering no evidence, or even what prompted those allegations. A spokesman for president Obama firing back, saying, neither the former president nor the Obama white house ordered or interfered with any such surveillance. This, following a dramatic and heated exchange, you see it there, inside the oval office with key aides. ABC's chief investigative correspondent Brian Ross leading us off tonight. Reporter: It was just before sunrise in palm beach, when the president of the United States took to Twitter to make one of his most stunning accusations ever. "Terrible. Just found out that Obama had my 'wires tapped' in trump tower just before the victory. Nothing found." Followed by four more presidential outbursts taking on president Obama and misspelling tap. "How low has president Obama gone to Tapp my phones during the very sacred election process. This is nixon/watergate. Bad (or sick) Guy!" Today, a senator from the president's own party, along with U.S. Intelligence officials, called it a troubling development. I am very worried. I'm very worried that our president is suggesting that the former president has done something illegal. Reporter: It would be a crime to reveal such a secret FBI wiretap on trump tower and no U.S. Official contacted by ABC news would confirm the allegation. It's an extremely serious offense. Anyone who would reveal the existence of a wiretap would violate federal law. Reporter: Because the president cited no proof, it is not clear tonight whether he based his allegations on a top secret white house briefing. Or whether it came from reading an article on the conservative Breitbart website, posted Friday, that detailed speculation from a conspiracy-loving talk show host mark Levin. How many of trump's people were eavesdropped on? How many had their conversations intercepted, recorded, transcribed? Because this, ladies and gentlemen, is the big scandal. Reporter: A spokesperson for president Obama quickly called the allegations false. And one of Obama's former national security aides, Ben Rhodes, responded to trump "No president can order a wiretap. Those restrictions were put in place to protect citizens from people like you." The president's Twitter rage today did serve to keep the focus on Russia, and contacts between the Russian ambassador and at least five top trump advisers. And it comes a day after a democratic member of the senate intelligence committee told ABC news that key wiretaps are part of the investigation although he said he has not read them. There are transcripts that provide very helpful, very critical insights into whether or not Russian intelligence and senior Russian political leaders including Vladimir Putin, were cooperating or colluding with the trump campaign at the highest levels to influence the outcome of our election. And chief investigative correspondent Brian Ross joins us live now. From what we know, there's a kernel of truth to what the president was saying, but he may have raised some serious legal issues. That's right. The FBI is investigating whether there was possible collusion between Russian spies and the trump campaign. And in cases like that, wiretaps can be used. But if anyone other than the president reveals the existence of a wiretap, that breaks the law. Legal experts tell us the president has the power to declassify anything he wants. A story still developing, all right, Brian, thanks so much.
This transcript has been automatically generated and may not be 100% accurate.