Washington (CNN) Attorney General William Barr has told federal prosecutors and law enforcement officials to involve top Justice Department officials at the start of investigations of 2020 political candidates to ensure "this fall's elections are conducted in a fair manner that is free from inappropriate influences."

The directive, outlined in a memo sent on Wednesday and obtained by CNN, is a sharp response to the charged investigations that marked the 2016 presidential cycle. Barr also told the officials to notify senior DOJ leaders when investigating illegal campaign contributions by foreign nationals.

It amounts to one of the most influential changes made in the wake of a Justice Department inspector general report that faulted the FBI for its handling of certain investigative steps as it probed potential ties between the Trump campaign and Russia. It also serves as reaction to the FBI's investigation of former Democratic nominee Hillary Clinton's email server, which was criticized for leadership decisions that were made out of Justice Department protocol.

"The Department has a strong interest in the prosecution of election-related crimes, including those involving corruption of the election process. Yet we must investigate and prosecute those matters with sensitivity and care to ensure that the Department's actions do not unnecessarily advantage or disadvantage any candidate or political party," Barr wrote in the memo, first reported by The New York Times.

The memo -- issued on the same day the Senate acquitted President Donald Trump in an impeachment trial over his pressure on Ukraine to dig up dirt on his political rivals -- will hold outsized influence given Trump's interest in investigating potential 2020 challenger and former Vice President Joe Biden.

At a contentious hearing before the House Judiciary Committee on Wednesday, FBI Director Christopher Wray would not say if he had been asked to open an investigation into Biden, but added that no one had told him to open any probe without "proper predication."

Barr had told reporters last month that he planned to initiate the requirement for signoff on the presidential investigations and that Wray had also approved of the development. The FBI chief's signoff would also be mandated, Barr had said.

At the hearing on Wednesday, Wray cited the new directive as one of the steps he's taking to reform the agency after the inspector general report.

The requirements will remain in effect through the 2020 election, after which the Justice Department will review its experiences and consider any changes, the memo says.

DOJ divisions and law enforcement agencies are also required to review their existing policies on the notification and consultation with senior officials for politically sensitive investigations and submit a summary report in two months.

According to the inspector general report, the Justice Department was not notified of the opening of the FBI's counterintelligence investigation into members of the Trump campaign, codenamed "Crossfire Hurricane," until two days after its launch.

It's unclear how high up at the FBI approval was given to the opening of the investigation.

In Wednesday's memo, Barr extended the directive to a candidate for vice president, as well as presidential campaigns and senior staff. Barr also said that investigations into candidates for the Senate or House of Representatives should be opened only with the notification and consent of an assistant attorney general and a US attorney.

In cases involving illegal contributions, donations or expenditures by foreign nationals to a campaign, Barr wrote, an assistant attorney general and US attorney will also need to be notified.

The campaign finance directive had direct parallels to a case that was unsealed in Manhattan last year, ensnaring two associates of Rudy Giuliani who helped the President's personal attorney in his endeavors in Ukraine.

The men, Soviet-born businessmen Lev Parnas and Igor Fruman, are said to have helped Giuliani as he sought political dirt from Ukraine. They have fought their campaign finance charges.

In the New York case, Barr and other senior officials at the Justice Department had been briefed on the investigation into the men, according to a DOJ official. However, the officials were not made aware until later, as the investigation progressed, that it had also begun to scrutinize Giuliani's role.

Barr told New York magazine last year that sensitive decisions should be made by politically appointed leaders, like the attorney general, because they are more accountable to the American people through elections.

"Career people are just as capable of acting politically with a small p, and I think, at the end of the day, if you're making a decision, it should be made by people who are accountable," Barr told the magazine.