Lindsey Graham vows Mueller will testify after op-ed on Trump's clemency for ally Roger Stone

South Carolina Republican has been one of the president's fiercest defenders on the Russia investigations

Senate Judiciary Chairman Lindsey Graham renewed his promise to call former special counsel Robert Mueller to testify about the origins of his Russia probe after Mr Mueller published an op-ed over the weekend defending it.

“Apparently Mr. Mueller is willing — and also capable — of defending the Mueller investigation through an op-ed in the Washington Post," Mr Graham said in a statement on Sunday. “Democrats on the Senate Judiciary Committee have previously requested Mr. Mueller appear before the Senate Judiciary Committee to testify about his investigation. That request will be granted."

Mr Graham was referring to a request from Democrat Senator Dianne Feinstein to interview Mr Mueller as part of the panel's probe into Justice Department procedures during its various Russia investigations from 2016 through 2019.

Mr Mueller's op-ed - prompted by Donald Trump's decision to commute the sentence of his 2016 campaign adviser and longtime ally Roger Stone on Friday - broke his long-held silence on recent criticisms among GOP ranks of his Russia investigation.

Mr Stone was convicted on five counts of lying to Congress earlier this year, charges that sprung from Mr Mueller's probe which spanned from 2017 to 2019.

Though he will avoid time in prison thanks to Mr Trump's commutation, Mr Stone remains a convicted felon, and "rightly so," Mr Mueller wrote in his rare op-ed for The Washington Post.

In addition to Mr Mueller's team, "Congress also investigated and sought information from Stone" in 2017, Mr Mueller wrote.

"A jury later determined he lied repeatedly to members of Congress. He lied about the identity of his intermediary to WikiLeaks. He lied about the existence of written communications with his intermediary. He lied by denying he had communicated with the Trump campaign about the timing of WikiLeaks' releases. He in fact updated senior campaign officials repeatedly about WikiLeaks. And he tampered with a witness, imploring him to stonewall Congress," Mr Mueller wrote, referring to Mr Stone's connection with Russian government agents who leaked hacked emails from the Clinton campaign to Wikileaks during the 2016 campaign.

"The jury ultimately convicted Stone of obstruction of a congressional investigation, five counts of making false statements to Congress and tampering with a witness. Because his sentence has been commuted, he will not go to prison. But his conviction stands," he added.

The former special counsel's investigation has come under increased scrutiny in the GOP-controlled Senate. The Judiciary, Homeland Security, and Financial Services Committees are investigating the origins of some federal law enforcement operations to counter Russian election interference headed by Obama-era officials at the FBI and Justice Department in 2016 and 2017.

Mr Trump, Judiciary Chairman Lindsey Graham, Homeland Security Chairman Ron Johnson, and other Republicans have accused those Obama-era officials of letting their personal liberal sympathies drive the investigations into possible ties between the 2016 Trump campaign and Russia.

Congressional Democrats have accused Republicans of attempting to re-write the history books to obscure the ethically questionable — and sometimes illegal — behaviour of Trump campaign officials uncovered by Mr Mueller.

In his op-ed, Mr Mueller wrote: "I feel compelled to respond both to broad claims that our investigation was illegitimate and our motives were improper, and to specific claims that Roger Stone was a victim of our office. The Russia investigation was of paramount importance. Stone was prosecuted and convicted because he committed federal crimes.

"We made every decision in Stone’s case, as in all our cases, based solely on the facts and the law and in accordance with the rule of law. The women and men who conducted these investigations and prosecutions acted with the highest integrity. Claims to the contrary are false."

Mr Graham commended the president's decision to commute Mr Stone's sentence on Friday, and also cast aspersions on the DOJ's counterintelligence operations against Russian election interference.

"In my view it would be justified if President [Trump] decided to commute Roger Stone's prison sentence. Mr. Stone is in his 70s and this was a non-violent, first-time offense," Mr Graham tweeted.

"Over time we learn how biased and corrupt Crossfire Hurricane and the Mueller probes were," the chairman added.

Mr Graham's views were not reflective of the entire Senate Republican conference.

Utah Senator Mitt Romney, the only Republican to vote to convict Mr Trump at his impeachment trial earlier this year, characterised the president's commutation of Mr Stone's sentence as "unprecedented, historic corruption".

The Justice Department's inspector general has issued several reports highlighting problems with the FBI's use of Foreign Intelligence Surveillance Act (FISA) warrants but has disputed Mr Graham's notion that political motives undergirded the direction of the bureau's operations.

The FBI's 2016 counterintelligence investigation into possible ties between the Trump campaign and Russia — nicknamed Crossfire Hurricane — “was opened for an authorized investigative purpose and with sufficient factual predication,” Mr Horowitz wrote in 2019.