Senior House Republicans formally alleged that "political considerations hijacked" the FBI's investigation of Hillary Clinton's use of a private email account and server in a letter to a pair of independent federal watchdogs.

"It appears increasingly clear that political considerations hijacked the criminal process in this case, and routine, longstanding policies and procedures were ignored," House Judiciary Committee chairman Bob Goodlatte, R-Va., House Oversight and Government Reform Committee chairman Jason Chaffetz, R-Utah, and 21 other lawmakers wrote in a Tuesday letter to the inspectors general for DOJ and the State Department. "As such, we request that you open an investigation into this matter at your respective Departments.

House Republicans have asked the independent auditors tasked with monitoring the State Department and the Justice Department to investigate "the special treatment given to key witnesses" in the Clinton email scandal. The FBI was wrong to let senior Clinton aides attend Clinton's FBI interview and claim to have "attorney-client privilege," despite not working as attorneys.

"Allowing them to sit in on Secretary Clinton's interview raises questions as to whether a serious interview of Secretary Clinton was ever even contemplated," the lawmakers wrote.

GOP investigators have been frustrated to learn of a variety of "side agreements" between the FBI and the Clinton team, such as immunity for former Clinton chief of staff Cheryl Mills and her deputy, Heather Samuelson. The aides were given immunity deals and allowed to destroy laptops following FBI review, for instance.

Goodlatte focused Tuesday on the decision to let Mills and Samuelson attend Clinton's FBI interview, even though they were presumably under investigation themselves, saying their attendance would allow the three women to coordinate their stories.

"[I]t offered Ms. Mills and Ms. Samuelson an opportunity to further corroborate their stories with the target of the FBI's investigation — Secretary Clinton — and have insight into questions being asked of Secretary Clinton regarding communications to which they may have been parties," the lawmakers wrote to State Department inspector general Steve Linick and DOJ inspector general Michael Horowitz.

They asked the independent investigators to find out why the FBI allowed Mills and Samuelson to be treated as Clinton's attorneys and for any information about whether the FBI considered that the aides had a conflict of interest.

"Ms. Mills and Ms. Samuelson were responsible for culling and shredding documents related to Secretary Clinton's tenure and, whether willfully or inadvertently, are responsible for the destruction of evidence and official records," Goodlatte and the other lawmakers wrote. "As such, they were key witnesses who could not have ethically provided legal representation to Secretary Clinton after their departure from the State Department."