The decision by Deputy Attorney General Rod Rosenstein to have the Justice Department’s inspector general look into possible FBI surveillance of President Trump’s 2016 campaign has failed to allay some Republican lawmakers' fears the agency is too tainted already to be trusted with an internal investigation.

Rosenstein agreed during a meeting with Trump and senior intelligence officials on Monday that the Justice Department should “expand its current investigation to include any irregularities with the Federal Bureau of Investigation’s or the Department of Justice’s tactics concerning the Trump Campaign,” according to a readout provided by the White House. The Justice Department’s internal watchdog originally launched a probe in March into the agency’s handling of a surveillance warrant for former Trump campaign Carter Page, following demands for an investigation by conservative lawmakers who felt the agency had overstepped its authority.

Some of those same lawmakers are now skeptical that the broadened inspector general probe will be handled in a timely and appropriate manner, or that the conclusion will deviate from what they already believe to be true.

“[W]e’ve seen disturbing evidence that the FBI engaged in political targeting, But the DOJ can’t be trusted to investigate themselves – Congress needs the documents too,” House Freedom Caucus Chairman Mark Meadows, R-N.C., said in a tweet Sunday evening, urging the agency to make available to Congress the same materials it plans to review as part of its internal investigation.

[Related: Second special counsel needed because DOJ can't 'investigate themselves']

Meadows, who joined two of his House colleagues last week in urging the president to intervene so the Justice Department would turn over the documents sought by congressional investigators, added on Monday that Rosenstein’s “belated referral” to the agency’s internal watchdog indicated he was aware of malpractice by the department and “he did nothing, or he’s seen the facts and believes nothing is wrong.”

The top conservative lawmaker is expected to help introduce a 12-page House resolution on Tuesday that details alleged misconduct at the Justice Department and FBI surrounding the Clinton email investigation, the Russia probe, and abuses of the Foreign Intelligence Surveillance Act.

More than a dozen GOP lawmakers have endorsed the resolution, which will call for a second special counsel to be appointed, according to a statement released by Rep. Lee Zeldin, R-N.Y., on Monday.

Rep. Matt Gaetz, R-Fla., also suggested on Monday that the Justice Department may be incapable of appropriately investigating itself, arguing during a Fox News appearance that appointing a second outside investigation was preferable and necessary since Attorney General Jeff Sessions remains recused from the Russia probe.

[Also read: Jeff Sessions still hesitant to appoint second special counsel to investigate FBI, DOJ]

“The consequence of that recusal is that Rod Rosenstein, the very individual who was signing renewals of the FISA warrants, now has the ability to send this latest allegation off to investigation land and then use that as a basis to not produce documents to Congress … ” Gaetz charged.

According to the White House, chief of staff John Kelly agreed on Monday to immediately organize a meeting between top intelligence and Justice Department officials and congressional leaders to review the information requested by Gaetz and his colleagues. Democrats had previously warned that Trump could use Rosenstein’s refusal to turn over the sensitive documents as a reason to fire him, and squeeze the ongoing special counsel investigation.

“The demand for additional information about the scope and other details regarding the special counsel’s ongoing investigation is ... misplaced,” said Sen. Dianne Feinstein, D-Calif., the top Democrat on the Senate Judiciary Committee. “Department regulations protect this type of information from disclosure to Congress for legitimate investigative and privacy reasons.”

Republican opposition to Rosenstein’s request for an expansion of the ongoing IG investigation comes just weeks after lawmakers similarly complained about Sessions’ decision to appoint U.S. Attorney John Huber to review allegations of FISA abuse, rather than create a second special counsel.

Trump’s legal team has also privately vented about the need for a second special counsel, a source close to the White House told the Washington Examiner. However, the president himself has yet to join Republican lawmakers who have complained about Rosenstein’s latest move.

In an interview Monday with Fox News’ Martha MacCallum, Vice President Mike Pence said Trump was “grateful” that the Justice Department asked the inspector general to “look into and determine and ensure that there was no surveillance done for political purposes against our campaign.”

Still, the president’s re-election campaign managed to fundraise off the development on Monday with an email to supporters headlined: " Worse than Watergate."

"THIS COULD BE THE GREATEST POLITICAL SCANDAL IN AMERICAN HISTORY," the email declared. "I need you to sign your name right this second to join me in demanding this abuse of power gets investigated."