The Senate Intelligence Committee said that they have found zero evidence to suggest Trump Tower was wiretapped. President Trump has made the allegation that the Obama White House ordered the action, which sent Congress scrambling for answers and evidence.

Based on the information available to us, we see no indications that Trump Tower was the subject of surveillance by any element of the United States government either before or after Election Day 2016," said Sens. Richard Burr (R-NC) and Mark Warner (D-VA), who serve ad the chairman and ranking member respectively of the senate Intelligence Committee.

Rep. Devin Nunes (R-CA), who chairs the House Intelligence Committee, said there is no physical evidence of a wiretap, but added that the tower could have been under surveillance (via Washington Examiner):

House Intelligence Committee Chairman Devin Nunes, R-Calif., pushed back against his Senate counterparts' categorical conclusion that Trump Tower was never under surveillance during the campaign or presidential transition. Nunes stood by his Wednesday assertion that there was no "physical" wiretap on then-candidate and President-elect Trump. But beyond that, he said, is unknowable. […] There was no physical wiretap on Trump but "you can't rule out surveillance because we know for a fact that they picked up incidental collection on General Flynn—now we don't know if that was it," Nunes told reporters on Thursday.

Former Attorney General Michael Mukasey told ABC News’ Martha Raddatz that Trump is probably right to think that Trump Tower was under surveillance, but added that the president was wrong to accuse Obama of being behind the action.