A senior Democratic politician has defended his demand for an independent investigation into possible links between the president and Moscow, saying: “We don’t know what the Russians have on Donald Trump.”

Minnesota senator Al Franken, whose questioning of Jeff Sessions was the initial trigger that set in motion the decision by the Attorney General to recuse himself from overseeing an FBI probe, said Mr Trump’s calls for Barack Obama to be investigated were nothing more than a distraction.

“This is just a distraction, to distract from this very, very serious interference by a foreign power on our democracy and the question of whether Trump world - his campaign, his business associates - had anything to do with it and colluding with them,” he told ABC News.

He spoke after Mr Trump set Twitter alight once again at the weekend with a claim - made without providing any evidence to support it - that Mr Obama had tapped his phones at Trump Tower ahead of the election. Mr Trump demanded that the Congress include this allegation as part of their probe, something they appear likely to do.

Mr Obama issued a statement saying he has not ordered such phone tapping. National security experts said that for the FBI to carry out such a move, it would require a warrant from a Foreign Intelligence Surveillance (FISA) court and for a judge to believe there were grounds to believe a US location was being used to benefit a foreign power, or else commit a crime.

Reports as to whether such as warrant was issued are unclear. Most US media says officials believed Mr Trump made the claim not after receiving new intelligence but after reading a repot on the right wing Breitbart News site.

John Oliver names Trump-Russia scandal ‘Stupid Watergate’

Mr Franken said he wanted an independent probe to look into Russia’s alleged interference in the US election and alleged links between Russia and members of Mr Trump’s team.

The president has repeatedly denied that any such links exist and has denounced intelligence leaks that suggest to the contrary.

“His own son, Donald Trump's son, has said in 2008, that Russia did an inordinate amount of business with them. And we don’t know what they have over him,” said Mr Franken, a member of the Senate Judiciary Committee.

Loading....

“We don't know what the Russians have on Donald Trump. And we need - and we need to see, if anything - we need to see his tax returns.”

Mr Sessions had told Mr Franken under oath that he had not had any contact with Russian officials. He later admitted he had twice met with Russian Ambassador Sergey Kislyak.

“That turned out not to be true,” said Mr Franken, speaking on Sunday. “He was testifying under oath to the American people and he said something that just wasn’t true.”

Yet Mr Franken has stopped short of calling for Mr Sessions to resign, something that other senior Democrats have done.