Donald Trump is "impeachable" and Congress must look at the question again in the wake of the Mueller report, the Republican former governor Bill Weld has said.

Mr Weld is running against Mr Trump in the Republican 2020 primary, much to the chagrin of the White House – but when he talks about impeachment he knows more than most.

The former federal prosecutor worked on the House of Representative’s 1974 impeachment inquiry of Richard Nixon and contributed to then House’s report on the constitutional grounds for impeachment He also resigned as head of the Justice Department’s criminal division in 1988 amid concerns over the ethical conduct of attorney general Edwin Meese.

“He just wants to interfere with the ordinary workings of the constitution and that’s quintessential impeachment offence,” Me Weld told MSNBC.

Mr Weld said that the 11 instances of possible obstruction of justice by Mr Trump that special counsel Robert Mueller laid out in his report into Russian election interference and the conduct of the Trump presidential campaign marks a “clear case of obstruction of justice”.

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The former governor also referenced a letter signed by more than 500 former prosecutors, including Mr Weld, that said the president should face charges.

“Each of us believes that the conduct of President Trump described in Special Counsel Robert Mueller’s report would, in the case of any other person not covered by the Office of Legal Counsel policy against indicting a sitting President, result in multiple felony charges for obstruction of justice,” the statement reads.

US senator Richard Blumenthal said he was “proud” to add his name to the list of signatures, which includes officials who worked for both Democratic and Republican administrations stretching back to Dwight Eisenhower.

When asked about the contention put forward by many Republicans that there was no conspiracy on show, Mr Weld was forthright that the actions of Mr Trump and attorney general William Barr prove otherwise.

“There was a [chargeable conspiracy],” Mr Weld said. “I think it’s clear that my old friend Bill Barr said to my old friend Bob Mueller: ‘I’m not going to let you charge this guy if you do I’m going to squash it’ so Mueller had no recourse”.

Mr Weld said that he had been against impeachment proceedings but that the “i word deserves re-examining”.

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He said that Mr Barr’s actions, in refusing to be appear in front of a House committee to discuss the report only hardened his resolve.

“If the president and the AG are simply going to thumb their nose at Congress and say ‘we aren’t going to play’... I think it needs a little re-thinking in view of the brazenness of the response”

Being pro-choice and campaigning against climate change Mr Weld bears little resemblance to the Republican Party now led by Mr Trump, indeed he was on the Libertarian Party ticket for the 2016 presidential election.

Mr Weld hopes to give Mr Trump a bloody nose in early primary races, particularly New Hampshire, with the aim of getting some momentum to challenge the president.