GOP lawmakers returning to Washington are signaling they intend to step up their campaign to look into alleged spying by FBI agents on 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's 2016 campaign.

The effort comes as Democrats ramp up their own investigations into the Trump administration and could serve as a bit of GOP counterprogramming to put the spotlight on what Republicans contend is suspicious behavior under the Obama administration.

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Two Senate chairmen previewed the coming GOP efforts with a recent letter to 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, who raised eyebrows when he publicly asserted he believed the Trump campaign was spied on and said he would review the intelligence community’s actions to ensure no improper surveillance occurred.

Democrats were surprised and angered that Barr used the word "spying" to describe surveillance the FBI did during its investigation of Russia’s interference in the 2016 presidential election, accusing him of promoting a GOP talking point.

In a letter sent to the attorney general on Thursday, Sens. 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) and 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.) asked the Department of Justice (DOJ) for a briefing on Barr’s review and cited text messages between former FBI agent Peter Strzok and former FBI attorney Lisa Page that they described as exhibiting "potential attempts by the FBI to conduct surveillance of President-elect Trump’s transition team."

"Any improper FBI surveillance activities that were conducted before or after the 2016 election must be brought to light and properly addressed," wrote Grassley and Johnson, who chair the Senate Finance and Homeland Security committees, respectively. They also raised concerns about potentially unauthorized Justice Department leaks to the press about the Russia investigation.

Lawmakers on the House and Senate Judiciary committees will have an opportunity to grill Barr in back-to-back open hearings this week as he testifies on 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 investigation and final report, a redacted version of which Barr released roughly a week ago.

Barr is expected to face considerable scrutiny from Democrats who accuse him of bias in his handling of Mueller’s report, which did not establish conspiracy between members of the Trump campaign and Russia but explicitly did not exonerate the president on allegations of obstruction. The attorney general is also likely to be questioned by Republicans about his plans to review the decisions in the FBI’s original Russia counterintelligence probe.

"I have loads of questions for Barr about origination of the spying and DOJ leaders' role in the spying," Rep. Andy Biggs (R-Ariz.), a member of the House Judiciary Committee, told The Hill on Friday, adding that he has "lots of questions" following the release of Mueller’s report.

Republicans have long suggested FBI agents were politically motivated in opening the investigation into the Trump campaign, citing text messages exchanged by officials who worked on the Russia and Clinton email investigations in which they criticized Trump’s candidacy. House Republicans led an investigation into the FBI’s handling of the Russia and Clinton probes that was quietly shuttered last year, shortly before Democrats took control of the lower chamber.

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GOP lawmakers have also alleged the FBI abused its surveillance authorities by relying on information from the author of the controversial Trump-Russia dossier, which was in part funded by Democrats, to justify a surveillance renewal application to wiretap former Trump campaign adviser Carter Page.

Democrats have roundly rejected Republicans’ claims, accusing them of trying to undermine Mueller’s investigation, which concluded in March after 22 months.

The Justice Department’s inspector general is currently investigating the FBI’s compliance with the law and procedures with respect to the Page warrant application, a review Barr expects to be completed as soon as next month.

Barr said in congressional testimony earlier in April that he plans to initiate his own review of the "genesis and the conduct" of intelligence collection directed at members of the Trump campaign based on what Inspector General Michael Horowitz finds; Barr said it was important to determine whether the surveillance was "adequately predicated."

The developments come against the backdrop of Trump’s own public pronouncements criticizing the Russia probe as an attempted "coup" and casting Mueller’s investigators as "Trump haters." The president has also cheered Barr, who became his second attorney general in February, for signaling he will set up a team to review Horowitz’s findings to potentially find avenues of further 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.), an ally of the president, has also forecast his own plans to review whether the FBI abused the Foreign Intelligence Surveillance Act in applying for the warrant to surveil Page while dismissing Democrats’ efforts to probe possible obstruction by the president as a predicate for a "stampede to impeach" Trump in an interview with Fox News’s Sean Hannity Sean Patrick HannitySunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Cruz: Trump should nominate a Supreme Court justice next week Ex-Pence aide: Trump spent 45 minutes of task force meeting 'going off on Tucker Carlson' instead of talking coronavirus MORE last week.

In addition to probing the episodes of potential obstruction laid out in Mueller’s report, House Democrats have unveiled a flurry of investigations into Trump and his administration with their newfound majority powers, looking at everything from security clearances to the president’s finances.

House Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffPelosi, Democrats unveil bills to rein in alleged White House abuses of power Chris Matthews ripped for complimenting Trump's 'true presidential behavior' on Ginsburg Trump casts doubt on Ginsburg statement, wonders if it was written by Schiff, Pelosi or Schumer MORE (D-Calif.) has also pledged to further investigate Trump’s ties to Russia, including financial interests, to ensure Trump is not compromised by the Kremlin or another foreign power.

Mueller’s exhaustive 448-page report, which was redacted to conceal information told to the grand jury, classified material, and details about ongoing investigations and third parties, makes only passing mention of the so-called dossier compiled by former British intelligence agent Christopher Steele.

The research, which BuzzFeed published in early 2017, is repeatedly described by Mueller as a set of "unverified allegations." The report leaves many of the salacious allegations in the dossier unproven.

Rep. John Ratcliffe John Lee RatcliffeDemocrats call for declassifying election threats after briefing by Trump officials Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings FBI chief says Russia is trying to interfere in election to undermine Biden MORE (R-Texas), a member of the House Judiciary Committee, signaled recently that he plans to ask Barr and potentially Mueller, who has also been invited to testify by the lower chamber, about his report’s scant mentions of Steele’s work or the firm that hired him, Fusion GPS.

"And a lot of folks have questions about that. Did he look at any of that? Why did his report not mention Fusion GPS? Why did it not mention the Steele dossier, all of the things that go to the troubling origin here?" Ratcliffe said in an interview on Fox News.

"I know members of Congress are looking forward to asking questions of both Attorney General Barr and special counsel Mueller because they will provide the clarity that the people need to see how all of this started when it shouldn't have started in the first place," Ratcliffe said.

A heavily redacted version of the Page warrant applications were released by the Justice Department last year, and Trump has pledged to declassify and release a fuller version of the documents, though some foreign allies have raised concerns over that effort.

The documents showed the FBI informed the Foreign Intelligence Surveillance Court that officials believed Steele had been hired by someone looking for information to discredit Trump but noted the bureau thought his information to be credible based on his past assistance. Republicans have accused the FBI of not sufficiently disclosing the research’s link to Democrats.

Mueller’s report includes a footnote mention of the warrant on Page, stating that the warrant was based on a "finding of probable cause to believe that Page was an agent of a foreign power." The special counsel did not ultimately bring charges against Page for acting as a foreign agent, which the report states would have required meeting the higher standard of producing sufficient evidence to prove beyond a reasonable doubt that Page acted as a Kremlin agent during the period at issue.

Juliegrace Brufke contributed.