Donald Trump may have commuted Roger Stone’s prison sentence but the President’s long-time ally remains a convicted criminal, former Special Counsel Robert Mueller said on Saturday.

Mr. Stone, 67, had been set to begin serving a 40-month prison term on Tuesday after his conviction on seven felony charges originally brought by Mr. Mueller as part of the Russia collusion probe.

Multiple charges

The charges include tampering with a witness and obstructing the House investigation into whether the Trump campaign conspired with Russia to help him win the 2016 election.

In an op-ed piece in The Washington Post on Saturday, Mr. Mueller defended his probe as being of “paramount importance,” dismissing White House claims that he was out to get Mr. Trump and those who worked with him. “Stone was prosecuted and convicted because he committed federal crimes. He remains a convicted felon, and rightly so,” Mr. Mueller wrote as Democrats — and two Republican Senators — piled on Mr. Trump for again intervening in the justice system to help an ally.

Senator Mitt Romney, who infuriated Mr. Trump when he became the only Republican to vote to convict the President in his impeachment trial, pulled no punches on Saturday. “Unprecedented, historic corruption: an American President commutes the sentence of a person convicted by a jury of lying to shield that very President,” he tweeted.

‘A mistake’

Another Republican Senator, Pat Toomey, also criticised Mr. Trump but in milder terms, saying that as Mr. Stone has been duly convicted it was “a mistake” to commute his sentence.

Most Republicans have remained largely mute on the matter, while Democratic critics led by House Speaker Nancy Pelosi unanimously condemned Mr. Trump. “President Trump’s decision to commute the sentence of top campaign advisor Roger Stone, who could directly implicate him in criminal misconduct, is an act of staggering corruption,” she tweeted. Ms. Pelosi called for legislation “to ensure that no President can pardon or commute the sentence of an individual who is engaged in a cover-up campaign to shield that President from criminal prosecution.”

Democratic presidential candidate Joe Biden weighed in without mentioning Mr. Stone by name. “I’ve said it before, and I’ll say it again: Donald Trump is the most corrupt President in modern American history,” he tweeted. “Every day that he remains in office, he further threatens the future of our democracy. We have to vote him out this November,” wrote Mr. Biden.