Washington CNN —  

Sen. Kamala Harris Thursday asked Attorney General William Barr to clarify whether President Donald Trump ever pressured Barr to open an investigation into any individual.

The letter comes hours after Trump called for former Secretary of State John Kerry to be prosecuted for violating the Logan Act by negotiation with the Iranian government – a charge Kerry immediately denied.

Barr waffled last week when Harris asked him at a Senate Judiciary Committee hearing if Trump had ever asked him to open an investigation into anyone.

In the letter to Barr, Harris, who is running for president, wrote, “Today, the President all but confirmed that he has made such a request when he called publicly for the prosecution of a former Cabinet secretary and then stated that his ‘people’ disagreed with him.”

“In light of the President’s deeply troubling statements, I request that you supplement your testimony and clarify your answers to my question,” Harris’ letter reads.

During Barr’s contentious congressional hearing, Harris asked, “Has the President or anyone at the White House ever asked or suggested that you open an investigation of anyone. Yes or no, please, sir.”

Barr said, “Um, the President or anybody else…”

“Seems you’d remember something like that and be able to tell us,” Harris said.

“Yeah but I’m trying to grapple with the word ‘suggest,’” Barr replied. “I mean, there have been discussions of matters out there that they have not asked me to open an investigation, but –”

“Perhaps they’ve suggested?” Harris followed up.

“I don’t know, I wouldn’t say suggest –” Barr said.

“Hinted?” Harris asked.

“I don’t know,” Barr said.

“Inferred? You don’t know. OK,” Harris said.

It was one of the most contentious and stand out moments from a long day of testimony for Barr on Capitol Hill. Harris called on Barr to resign following the hearing.

Harris followed up on that line of questioning on Thursday by demanding Barr respond definitively to the question.

Harris wrote, “In order for the American people to retain trust in the Department of Justice, the public must have confidence that the women and men who enforce our laws act with fairness and impartiality.”

“Your failure to categorically respond to my question in the negative undermines that confidence,” Harris continued.

Harris cited special counsel Robert Mueller’s report into Russian interference in the 2016 US presidential election and exploration of potential obstruction of justice by the President as a reason behind her request. She wrote Trump asked then-Attorney General Jeff Sessions three times to open an investigation into his former opponent, Hillary Clinton.

“Among the potentially obstructive acts examined by the Special Counsel were repeated attempts by the President to target his perceived opponents using the power of federal law enforcement.”

CNN’s Phil Mattingly contributed to this report.