WASHINGTON — An FBI agent who worked on separate investigations into Democrat Hillary Clinton and President Donald Trump's campaign testified behind closed doors to two House committees Wednesday as Republican lawmakers stepped up efforts to highlight what they say is bias at the Justice Department.

The agent, Peter Strzok, exchanged anti-Trump texts with a colleague, FBI lawyer Lisa Page, as both worked on the Clinton investigation and briefly on special counsel Robert Mueller's investigation into alleged ties between Trump's campaign and Russia. House Republicans have seized on the texts as part of investigations into the Justice Department, the FBI and decisions that both made during the 2016 presidential election.

In one of the texts, from August 2016, Strzok wrote, "We'll stop it," in reference to a potential Trump election win.

The barrage of Republican criticism against the Justice Department comes just a few months before the midterm elections and amid intense sparring between the parties over the FBI's role in the Russia probe. The House is expected to vote Thursday on a resolution demanding that the department hand over thousands of documents that Congress has requested by July 6. The resolution was approved by the House Judiciary Committee.

Democrats have accused Republicans of trying to undermine Mueller's investigation for political gain.

Trump criticized the closed-door interview with Strzok, saying it should be "shown to the public on live television, not a closed-door hearing that nobody will see."

House Judiciary Committee Chairman Robert Goodlatte, R-Va., has said there will also be a public hearing with Strzok. The Judiciary and House Oversight and Government Reform committees are conducting the investigation.

A seasoned counterintelligence agent, Strzok had a leading role on the investigation into whether Clinton illegally mishandled classified information through her use of a private email server while she was secretary of state. He later joined Mueller's team investigating Russian election interference, but he was reassigned last summer after the discovery of anti-Trump text messages he had traded with the Page, who had already left Mueller's team.

The Republicans' charges of bias were bolstered earlier this month by a report by the Justice Department's internal watchdog that faulted top department officials, including former FBI Director James Comey, for their handling of the probe of Clinton's emails. The report also detailed the communications by Strzok and others criticizing Trump.

While strongly criticizing the way the Clinton investigation was handled, the inspector general ultimately found no evidence that bias affected the decision not to charge her.

Strzok was recently escorted from the FBI building as his disciplinary process winds through the system, his attorney has said. He "remains a proud FBI agent" who wants to serve his country but has been the "target of unfounded personal attacks, political games and inappropriate information leaks," according to a statement last week from the lawyer, Aitan Goelman.

Rep. Mark Meadows, R-N.C., one of the most vocal critics of the Justice Department, said as he walked into the interview that he had several questions about the beginning of the Russia investigation in 2016 and the informants who were used to question Trump campaign staff.

"Ultimately you cannot have bias within the FBI and DOJ [the Justice Department] and expect justice to be meted out evenly," Meadows said.

The Strzok interview is one of several events this week in which House Republicans are criticizing the Justice Department. At a contentious session Tuesday, the Republican-led Judiciary panel approved the resolution requesting that the department provide documents, despite an existing agreement to do so that was announced by the office of House Speaker Paul Ryan, R-Wis., over the weekend.

Meadows and Rep. Jim Jordan, R-Ohio, two vocal critics of the Clinton investigation, were behind the resolution, which wouldn't be enforceable but would send a strong message to Justice Department officials.

The Justice Department and the FBI have already turned over more than 800,000 documents to congressional committees, but subpoenas from the Justice and Intelligence panels are demanding additional materials. Lawmakers have threatened to hold top Justice Department officials in contempt or impeach them if the documents aren't turned over.

On Thursday, FBI Director Christopher Wray and Deputy Attorney General Rod Rosenstein will appear at an open hearing to testify about both investigations and the documents Republicans are seeking. Goodlatte said that he intends to use Thursday's hearing to question Wray and Rosenstein about complying with the requests and that he encouraged "others to do the same."

Democrats angrily fought the resolution approved Tuesday.

Reps. Jerrold Nadler of New York and Elijah Cummings of Maryland, the top Democrats on the Judiciary and Oversight committees, respectively, accused Republicans after the interview of "desperately trying to find something — anything — to undermine" Mueller's investigation.

"The special counsel's investigation has already uncovered evidence to support indictments against 20 individuals and five guilty pleas," they said in a statement. "His work stands on its own, in a court of law, and Republicans should stop trying to undermine it."