Sen. Lindsey Graham is urging the leaders of the United Kingdom, Italy, and Australia to cooperate with the Justice Department in its broad inquiry into how the Trump-Russia investigation began.

The Senate Judiciary Committee chairman sent a letter on Wednesday after it was revealed Attorney General William Barr and U.S. Attorney John Durham made contact with officials in these three countries, offering a full-throated endorsement of the "investigation into the investigators" as reports describe it as a campaign to discredit special counsel Robert Mueller's investigation.

Calling it an "important" inquiry that is "well within the bounds of his normal activities," Graham urged British Prime Minister Boris Johnson, Italian Prime Minister Giuseppe Conte, and Australian Prime Minister Scott Morrison to "continue cooperating with the U.S. Attorney General" and highlighted how their countries "routinely exchange law enforcement information with each other to assist in the course of investigations."

"He is simply doing his job," Graham said.

The South Carolina Republican claimed U.S. law enforcement and intelligence officials relied on foreign intelligence as part of their efforts in monitoring President Trump's campaign, citing three specific examples: the use of an anti-Trump dossier compiled by British ex-spy Christopher Steele to obtain electronic surveillance warrants; a tip from former Australian diplomat Alexander Downer about Trump campaign adviser George Papadopoulos telling him the Russians had damaging information on former Secretary of State Hillary Clinton; and the actions of mysterious Maltese academic Joseph Mifsud, who allegedly told Papadopoulos that Russia had “dirt” on Clinton.

The letter comes amid a political firestorm over a phone call that Trump had on July 25 with Ukrainian President Volodymyr Zelensky. That phone call ended up being a central tenet of an August whistleblower complaint that raised concerns about a possible effort to pressure Ukraine to investigate former Vice President Joe Biden by leveraging millions of dollars of security aid. Although Trump claims there was no quid pro quo, his admission that he did discuss Biden with Zelensky prompted House Speaker Nancy Pelosi to announce an impeachment inquiry last week.

It was also revealed this week that Trump urged foreign leaders, including Zelensky and Morrison, to cooperate with Barr.

During a Fox News interview on Monday, Graham warned there was an effort underway to "shut down" Barr's inquiry, which is being led by Durham. Graham also openly wondered whether the intelligence official who filed the whistleblower complaint and his or her sources may be a focus of Barr's work.

"What about whether or not the whistleblower or people around the whistleblower were tied to the folks that opened up the investigation against Trump to begin with? We'll see," he said.