FBI Director Christopher Wray faced heated questions Thursday from House Republicans concerned that top officials in his agency are “tainted by bias” – in connection with both the 2016 Hillary Clinton email probe and ongoing Russia meddling probe – though the bureau boss cited an ongoing investigation as he repeatedly declined to address their complaints in detail.

“It’s important that we not jump first and ask questions later,” Wray told lawmakers on the House Judiciary Committee.

The hearing came as his bureau comes under rhetorical assault from President Trump – who appointed Wray to succeed ousted James Comey – and his Republican allies on Capitol Hill.

Sparking fresh outrage was the revelation over the weekend that FBI official Peter Strzok was removed from Special Counsel Robert Mueller’s probe over the summer for allegedly exchanging anti-Trump texts with an FBI lawyer with whom he was romantically involved. Both worked at one time on the Mueller investigation.

“Investigations must not be tainted by individuals imposing their own personal political opinions,” committee Chairman Bob Goodlatte, R-Va., said. “We do not know the magnitude of this insider bias on Mr. Mueller’s team nor do we have a clear understanding of the full magnitude of bias reflected in the Russia investigation and prior Clinton email investigation. … One thing is clear, though – it is absolutely unacceptable for FBI employees to permit their own political predilections to contaminate any investigation.”

Asked what he’s doing to ensure the top ranks of the bureau are cleared of those “tainted by bias,” Wray said he’s respecting an inspector general investigation underway covering the handling of last year’s Clinton email investigation. He said when he receives the findings, he will take “appropriate action as necessary” – and stressed that decisions must be made “based on nothing other than the facts” and the law, “not political considerations.”

Republicans have focused as much on the Clinton probe as they have on Mueller’s investigation that has ensnared members of Trump’s 2016 campaign circle. They are particularly focused on concerns that Strzok changed Comey’s early draft language describing Clinton’s actions regarding her private email server from “grossly negligent” to “extremely careless.”

Wray confirmed at Thursday’s hearing that “gross negligence” is a key legal standard for potential criminal consequences.

But when Goodlatte asked whether that language was changed to ensure Clinton could not be held liable under the Espionage Act, Wray deferred to the ongoing IG probe and would not comment.

“I leave it to others to conclude whether ‘extremely careless’ and ‘gross negligence’ [are] the same thing,” he said.

Goodlatte also spoke to GOP concerns about a double standard in the handling of the Clinton and Russia-Trump team investigations, asking why Clinton aides like Cheryl Mills did not face consequences in the private email server case.

Wray cited the IG investigation in declining to comment.

Rep. Jerry Nadler, D-N.Y., the top Democrat on the committee, attributed the mounting scrutiny on the bureau to the progress of the special counsel’s Russia probe, which led last week to a guilty plea for Trump’s ex-national security adviser Michael Flynn.

He predicted “attacks on the FBI will become more … brazen as the special counsel does his work and the walls close in.”

Trump over the weekend tweeted that the FBI’s reputation is in “Tatters” in the wake of the “dishonest” Clinton probe.

Several House Republicans also recently asked Wray for an investigation into the FBI’s treatment of Clinton and then-candidate Donald Trump during the 2016 campaign.

New revelations about members of Mueller’s team only fueled their concerns. After the Strzok reports, conservative advocacy group Judicial Watch released an email showing a Mueller deputy praised outgoing acting Attorney General Sally Yates after she was fired in January by Trump for refusing to defend his controversial travel ban.

The email, obtained by Judicial Watch through a federal lawsuit, shows that on the night of Jan. 30, Andrew Weissmann wrote to Yates under the subject line, “I am so proud.”

Wray's start as FBI head would have been difficult enough, even without the intense scrutiny of the Russia investigation. Since he was sworn-in Aug. 2, the U.S. has had two of the deadliest shootings in its modern history and a terror attack in Manhattan.

Trump's weekend tweets created a fresh dilemma for Wray. With his bosses, Attorney General Jeff Sessions and his deputy Rod Rosenstein, staying publicly silent, it fell to Wray to defend the agency. But FBI directors traditionally have been low-key and stoic -- with Wray's predecessor, James Comey, a notable exception. And Trump's firing of Comey while he led the Russia probe shows the risk of antagonizing the president.

Wray's defense, in an email to FBI employees this week, didn't directly mention Trump's comments, leaving some current and former officials wishing he had pushed back more forcefully.

Wray said he was "inspired by example after example of professionalism and dedication to justice demonstrated around the bureau" and urged agents to "keep focused on our critical mission" while constantly under a microscope.

In his opening statement at Thursday’s hearing, Wray also said there is “no finer institution” than the FBI and there are “no finer people” than those who work there.

Another issue for lawmakers looking closely at the agency is the controversial anti-Trump dossier that made its way to the FBI last year, and to what extent it may have been used to justify a surveillance warrant for a Trump associate.

Shortly before Thursday’s hearing, Goodlatte called on the DOJ and FBI to provide the panel with all information that was presented to the Foreign Intelligence Surveillance Court to, his office said, “allegedly obtain a warrant based on politically-motivated opposition research” – a reference to the dossier.

In a particularly heated exchange during the hearing itself, Rep. Jim Jordan, R-Ohio, said he believes Strzok is the one who took the application to the FISA court – claiming that could mean opposition research was used to spy on another campaign.

“That is as wrong as it gets,” Jordan said. “Tell us if I’m wrong, but I don’t think I am.”

Wray said he could not discuss the matter in detail.

Separately, House Intelligence Committee Chairman Devin Nunes, R-Calif., has threatened a contempt resolution against leaders in both the Justice Department and FBI if they don’t turn over key information related to the anti-Trump dossier and other issues. Republicans want to know what role Strzok played in that process.

Fox News has learned the DOJ is now in the process of reviewing and handing over Strzok’s text messages as well.

Fox News’ Greg Norman and The Associated Press contributed to this report.