The list now includes today's comments from FBI Director James Comey and NSA Director Mike Rogers, who said they'd seen no evidence to support the president's claims during testimony before the House Intelligence Committee.
Early March 4, while away at his Mar-a-Lago estate in Florida, Trump fired off his first tweet accusing Obama of wiretapping his phones at Trump Tower in New York during the election. Trump then posted three more tweets, comparing the allegations to President Richard Nixon's Watergate scandal.
A spokesman for Obama rebutted the claims later that same day.
In an interview last week, Trump clarified his tweets. "'Wiretap' covers a lot of different things," he told Fox News' Tucker Carlson. "I think you're going to find some very interesting items coming to the forefront over the next two weeks."
Those who've spoken out about the accusations also include the bipartisan leaders of both the House and the Senate, as well as the bipartisan leaders of both chambers' intelligence panels. In addition, some have gone a step further, saying there are no indications any kind of surveillance was conducted at Trump Tower at all.
Here's a look at what Washington's major players have said about the wiretapping allegations:
James Comey, FBI director"I have no information that supports those tweets." - March 20
Mike Rogers, NSA director"I have seen nothing on the NSA side that we engaged in any such activity." - March 20
Sen. Chuck Schumer, D-New York, Senate minority leader"Pres. Trump needs to retract his claim immediately." - March 20
Sen. Ted Cruz, R-Texas"I don't know what basis the president has for these allegations." - March 19
Sen. Richard Burr, R-North Carolina, and Sen. Mark Warner, D-Virginia, chairman and vice chairman of Senate Intelligence Committee, respectively"We see no indications that Trump Tower was the subject of surveillance by any element of the United States government." - March 16
Rep. Paul Ryan, R-Wisconsin, speaker of the House"I have seen no evidence of wiretapping." - March 16
Rep. Nancy Pelosi, D-California, House minority leader"We see no evidence to support his outrageous allegations." - March 16
Rep. Devin Nunes, R-California, chairman of House Intelligence Committee"We don't have any evidence that that took place. ... I don't think there was an actual tap of Trump Tower." - March 15
Rep. Adam Schiff, D-California, ranking member of House Intelligence Committee"I've seen no evidence that supports the claim that President Trump made that his predecessor had wiretapped he and his associates at Trump Tower." - March 15
Sen. Lindsey Graham, R-South Carolina"I don't know of any evidence where the FBI tried to obtain a warrant against the Trump campaign to wiretap them." - March 15
Sen. John McCain, R-Arizona"I have no reason to believe this is true." - March 12
Sen. Mitch McConnell, R-Kentucky, Senate majority leader"There's no evidence of that. I've not heard of it before." - March 9
Sen. Tom Cotton, R-Arkansas"I have seen no evidence of that." - March 8
James Clapper, former director of national intelligence"There was no wiretap against Trump Tower during the campaign conducted by any part of the National Intelligence Community." - March 6
Sen. Susan Collins, R-Maine"I see no evidence of what he has alleged." - March 5
Sen. Marco Rubio, R-Florida"I've never seen anything about that anywhere before." - March 5
Kevin Lewis, spokesperson for former President Obama"Neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen." - March 4
ABC News' Veronica Stracqualursi and Adam Kelsey contributed to this report.