Former New York City mayor Rudy Giuliani said on Sunday that his repeated imputations of a supposed scandal at the heart of the Robert Mueller investigation – which Donald Trump calls “Spygate” – amounted to a tactic to sway public opinion and limit the risk of the president being impeached.

In an interview with CNN "State of the Union" host Dana Bash, Rudy Giuliani said:  "Of course we have to do it to defend the president."

Dana Bash accused Giuliani  of being part of a campaign to undermine the Mueller investigation.  President Trump has repeatedly called the special counsel’s work a “witch hunt”, despite its producing five guilty pleas, including by three of his former aides, and evidence of Russian tampering in US elections.

Speaking on CNN's "State of the Union" Giuliani said:  "It is for public opinion.  Because eventually the decision here is going to be impeach or not impeach. Members of Congress, Democrats and Republicans , are going to be informed a lot by their constituents. And so our jury – and it should be – is the American people.

Commenting further , Giuliani said: "So Republicans largely, many independents, even some Democrats now question the legitimacy of [the Mueller investigation] .  Democrats I would suggest for their own self-interest, this is not a good issue to go into the midterms."

Trump, Giuliani and other allies claim reports that an FBI informant monitored links between Trump aides and Russia show there was a “spy” on the Trump campaign. Senior figures in the intelligence community have rubbished such claims by the White House.

The Arizona senator Jeff Flake, a  Republican critic of Trump, told NBC’s Meet the Press the “Spygate” claims were a “diversion tactic, obviously”.

Senator Flake added:  "There is concern that the president is laying the groundwork to [fire] Bob Mueller or [deputy attorney general Rod] Rosenstein. If that were to happen, obviously, that would cause a constitutional crisis."