Attorney General William Barr Bill BarrHarris faces pivotal moment with Supreme Court battle Hillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE's decision to tap a U.S attorney to dig into the origins of the Russia probe is throwing a curveball into investigative plans on Capitol Hill.

Barr has appointed a U.S. attorney in Connecticut with the responsibility of examining the origins of the FBI’s investigation into the Trump campaign, a move long clamored for by President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE and his conservative allies. But the decision comes as a trio of high-profile Senate Republicans are planning their own investigations into “spying” on the Trump campaign during the 2016 election and the FBI’s handling of the Clinton email probe.

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GOP senators stressed they back Barr’s decision, though they warned that it could hamper their own plans in Congress, where prior committee probes have been thrown into limbo as they’ve tried to get access to the same witnesses and documents being swept up in a Justice Department investigation.

Senate Judiciary Committee Chairman Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) stopped short of saying he would end his investigative plans when asked about the impact John DurhamJohn DurhamTop Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Durham aide resigns from Russia probe amid concerns over pressure from Barr: report Trump praises several Fox News shows at briefing for coverage of Russia probe MORE’s appointment will have on his panel, but said that lawmakers “need to be cautious” and “make sure we don’t get in his way.”

“I don’t want to impede his ability. I don’t want to jeopardize somebody subject to an investigation,” Graham told The Hill. “I want to make sure that oversight doesn’t get in the way of the prosecutor. ... We’ll have to be cautious and find our way forward.”

Sen. Ron Johnson Ronald (Ron) Harold JohnsonThe Hill's 12:30 Report: Ginsburg lies in repose CHC leaders urge Senate to oppose Chad Wolf nomination Top GOP senators say Hunter Biden's work 'cast a shadow' over Obama Ukraine policy MORE (R-Wis.), the chairman of the Senate Homeland Security and Governmental Affairs Committee, said he supports Barr’s move but signaled concern that a Justice Department investigation could add roadblocks to their ability to force individuals to respond to the GOP investigations on Capitol Hill.

“I hope it doesn’t hamper it. I’m supportive of the fact that the attorney general is looking into all potential problems, potential crimes,” he said. “But I just want to make sure it does not hamper congressional investigations because our purpose is about … public policy and informing the public.”

Asked about his previous concerns that a criminal investigation negatively impacts congressional probes, he added: “It does. It absolutely does. It prevents us from getting access … because they’ll say we can’t release that because it will affect our criminal investigation.”

The U.S. attorney’s office in Connecticut declined to comment on Durham’s appointment to oversee the Justice Department investigation, which was first reported by The New York Times.

During an appearance last month before the Senate Appropriations Committee, Barr suggested he was concerned about “spying” on the Trump campaign during the 2016 election and that the Justice Department was going to review the issue

“I am not saying that improper surveillance occurred. I am saying I am concerned about it and looking into it, that’s all,” he said April 10.

He subsequently appeared to tip his hand during his appearance before the Judiciary Committee earlier this month that he had tapped someone to look into the matter, telling senators: “Yes, I do have people in the department helping me review the activities over the summer of 2016.”

Republicans have long clamored to investigate the origins of the FBI’s probe into election meddling and the Trump campaign, which the president has repeatedly blasted as a “witch hunt.”

Graham, Johnson and Sen. Chuck Grassley Charles (Chuck) Ernest GrassleyThe Hill's 12:30 Report: Ginsburg lies in repose Top GOP senators say Hunter Biden's work 'cast a shadow' over Obama Ukraine policy Read: Senate GOP's controversial Biden report MORE (R-Iowa), the chairman of the Senate Finance Committee and a member of the Judiciary Committee, have also joined forces to “investigate the investigators" now that special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's probe has wrapped up.

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Grassley previously said that trying to probe the origins of the Russia probe during the previous Congress would have sparked accusations of trying to interfere in Mueller’s investigation. But he argued on Tuesday that there is room for both Congress and the Justice Department investigation, characterizing Barr’s decision as “very, very good news.”

“Of course we will,” he said, asked if senators would keep investigating amid the Justice Department investigation. “He’s going to investigate and if he finds something he can prosecute. We investigate, we can’t prosecute.”

Durham isn’t the only individual investigating the 2016 election. Republicans are also closely awaiting the results of Justice Department Inspector General Michael Horowitz’s investigation into whether the FBI followed protocols in the Foreign Intelligence Surveillance Act process, which is expected to touch on the Carter Page warrant application.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellFEC flags McConnell campaign over suspected accounting errors Poll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ky.) noted Horowitz’s investigation during a recent interview with Fox News’s Martha MacCallum, adding that “if he indicates that there was some suspicion around the opening of the investigation, Senator Graham might well decide that he wants to take a look at that.”

Graham told The Hill, ahead of reports of Durham’s appointment, that the inspector general would come testify before the Judiciary Committee about his findings, which he expected would be wrapped up by the end of the month.

“I’m going to let him do his thing first because he’s sort of the road map,” Graham said about Horowitz’s role. “That’s why I didn’t want to do anything to get in his way.”

It’s not the first time congressional committees have had to compete with a Justice Department probe.

The FBI, then headed by Director James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE, was running its probe into election interference and the Trump campaign while the Intelligence Committee was investigating the same issue and the Judiciary Committee flirted with an investigation of its own. Congressional investigations often cede jurisdiction to any concurrent federal investigations — a coordinating process called “deconfliction.”

Johnson said on Tuesday that while the Justice Department would likely focus on “prosecutable crimes,” congressional oversight has “different purposes” and could include “wrongdoing that doesn’t meet the level of prosecutorial crimes,” leaks or improper influence into a campaign that could be prime areas for congressional oversight.

“We just did this backwards. We should have started with congressional investigations unimpeded by criminal proceedings. Once we issued our reports then we could refer that to the criminal justice system,” Johnson said about the initial report on Russia’s election interference.

Asked if they were about to do it “backwards” again, he added, “Yes, but now we’re two years into this and the attorney general is going to have to hop on this. I wish the special counsel would have looked into all of the issues."

Graham on Tuesday appeared to outline potential areas where his focus could differ from the Justice Department, including addressing what if any legislation is needed in the wake of the 2016 election.

But he added that when “you’ve got oversight and prosecutions going on at the same time, that could be a very dangerous combination.”