President Donald Trump has accused former President Barack Obama of “wire tapping” Trump Tower before the 2016 presidential election.

Trump made the claims in a series of tweets that he posted early Saturday, although he offered no evidence to back up his allegations ― and a former adviser to Obama pointed out that presidents cannot order wiretaps.

“Terrible!” Trump wrote at 6.35 a.m. Eastern time. “Just found out that Obama had my ‘wires tapped’ in Trump Tower just before the victory. Nothing found. This is McCarthyism!”

Read Trump’s full set of tweets (story continues below):

Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism! — Donald J. Trump (@realDonaldTrump) March 4, 2017

Just out: The same Russian Ambassador that met Jeff Sessions visited the Obama White House 22 times, and 4 times last year alone. — Donald J. Trump (@realDonaldTrump) March 4, 2017

Is it legal for a sitting President to be "wire tapping" a race for president prior to an election? Turned down by court earlier. A NEW LOW! — Donald J. Trump (@realDonaldTrump) March 4, 2017

I'd bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election! — Donald J. Trump (@realDonaldTrump) March 4, 2017

How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy! — Donald J. Trump (@realDonaldTrump) March 4, 2017

Trump also called Obama a “Bad (or sick) guy!” and likened the alleged tapping of his New York base to the “Watergate” scandal, which brought down Republican President Richard Nixon.

It was a “cardinal rule” in the previous administration that the White House stayed out of investigations conducted by the Justice Department, a spokesman for Obama said Saturday.

“As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen,” Kevin Lewis said in a statement. “Any suggestion otherwise is simply false.”

It’s unclear whether Trump had any proof to substantiate the allegations or if he was referencing a classified briefing. However, some media outlets have suggested he sourced the information from an article that the far-right website Breitbart News ran Friday, claiming that Obama “sought, and eventually obtained, authorization to eavesdrop on the Trump campaign.” Steve Bannon left his position as Breitbart executive chairman to become the CEO of Trump’s campaign. Bannon is now the White House’s chief strategist.

Per an official, I've confirmed that several people at the White House have been circulating this Breitbart story. https://t.co/WT4bdWNhSK — Robert Costa (@costareports) March 4, 2017

Other media commentators were keen to point out that the alleged wire taps that Trump “just found out” about had actually been reported on “for weeks.” The Guardian reported in January that the FBI had applied for a warrant under the Foreign Intelligence Surveillance Act to monitor Trump associates in the summer, but was rejected.

1/ The wiretaps that Donald Trump "just found out" about have been reported for weeks. I'm going to summarize here some of the discussion. — Justin Hendrix (@justinhendrix) March 4, 2017

4/ Republicans who have defended surveillance powers are now critical of it especially following Flynn's resignation https://t.co/bRVcxF9jlF pic.twitter.com/PgYLhfj1bQ — Justin Hendrix (@justinhendrix) March 4, 2017

The Trump Foundation gave $10,000 to conservative activist James O’Keefe’s Project Veritas, which works closely with Breitbart and is an unofficial arm of the Trump campaign. Ironically, Project Veritas did actually attempt to infiltrate the campaign of rival candidate Hillary Clinton. It successfully infiltrated outside groups aligned with it, secretly recording and then publishing internal campaign details, which Trump used repeatedly on the stump.

The tweets come after multiple investigations into Russian interference in the election. The CIA, FBI and National Security Agency concluded that operatives for Russian President Vladimir Putin did intervene during the campaign.

Trump’s administration is under mounting pressure over its alleged communications with Russian officials in the weeks before Trump officially entered the White House.

National security adviser Michael Flynn was forced to resign just 24 days into the role over allegations that he’d discussed U.S. sanctions against Russia with its ambassador in the lead-up to Trump taking office.

This week, it was widely reported that Attorney General Jeff Sessions met with Russian officials during the presidential campaign, even though he’d previously denied doing so, under oath, to the Senate Judiciary Committee. Sessions has since recused himself from the Russia investigations.

This article has been updated with more details, including comment from Kevin Lewis.

