PALM BEACH, United States (AFP) — The White House yesterday called for Congress to follow up on President Donald Trump’s explosive and unsubstantiated allegation that Barack Obama tapped his phone during last year’s election campaign.

Twenty-four hours after Trump’s incendiary claim, his aides scrambled to limit the political fallout — admitting it was still unproven and calling on Congress to investigate.

Citing still undefined “reports” of “politically motivated investigations”, press secretary Sean Spicer said Trump was calling on Congress to “determine whether executive branch investigative powers were abused in 2016”.

Trump spokeswoman Sarah Sanders echoed those comments.

“If this happened,” she told ABC, “this would be the greatest abuse of power and overreach that has ever occurred in the executive branch.”

Trump, who was taking “meetings and phone calls” at his golf course in West Palm Beach, Florida, has not commented publicly on the allegations.

On Saturday, he tweeted: “How low has President Obama gone to tap my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!” He provided no evidence to back up this claim.

Watergate is the generic term for the scandal that brought down President Richard Nixon in 1974. It began with the revelation of a secret wiretap in offices of the Democratic National Committee at the Watergate Hotel.

President Barack Obama, via a spokesman, denied Trump’s new allegation as “simply false”.

US presidents cannot legally order such wiretaps, which require the approval of a federal judge and reasonable grounds for suspicion.

Obama’s director of national intelligence James Clapper told NBC there was “no such wiretap activity mounted against the president-elect at the time as a candidate or against his campaign”.

Trump comments appeared to have been based on unverified claims made by the right-wing Breitbart News outlet. His chief strategist Steve Bannon used to run it.

Previous media reports have indicated that US prosecutors investigated communications between a server registered to the Trump Organization and a Russian bank.

As president, as candidate and as a showman, Trump has repeatedly embraced conspiracy theories, including the suggestion that Obama was not born in America. He was born in Hawaii, a US state.

He levelled the latest charges in a string of tweets early Saturday, at the end of a week in which his administration was battered by controversy over links between his advisors and Russian officials.

Trump was said to be furious that good reviews of his maiden speech to Congress on Tuesday were overtaken by a series of revelations about aides’ meetings with Russian officials.

The president was also said to be angry that Attorney General Jeff Sessions recused himself from any campaign or Russia-related investigations.

Sessions’ recusal came after it emerged that, speaking under oath during his Senate confirmation hearings about campaign contacts with Russia, he did not disclose two meetings with Moscow’s ambassador in Washington.