"Any other government workers who engaged in such serious offenses would, at a minimum, have their clearances suspended pending an investigation. The failure to do so has given the public the impression that Secretary Clinton and her associates received special treatment," Grassley wrote in the letter.

He added that he had asked State Department staff under the Obama administration if Clinton or her staff had their security clearances removed, but they declined to tell him.

"It is unclear what steps the State Department has taken to impose administrative sanctions," Grassley wrote in his letter.

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Grassley wants to know if Tillerson agrees with the FBI's findings that Clinton was "extremely careless" with classified material, if a "reasonable person" in Clinton's position should have known how to handle classified material and that other individuals are "often subject to security or administrative sanctions."

The Iowa senator also wants to know if, as a result of the FBI investigation, the State Department has started a review of the security clearances of Clinton or her aides, or if any of them have had their security clearance removed.

Grassley's committee sent a flurry of emails to the Obama-era State Department asking for details on Clinton and her staffers as part of its investigation into Clinton's use of a private email server for State business.

Grassley's investigation drew him scorn from top Democrats including then-Minority Leader Harry Reid Harry Mason ReidSenate Republicans signal openness to working with Biden Mellman: The likely voter sham Bottom line MORE (D-Nev.), who questioned in late 2015, "How much taxpayer money is Senator Grassley wasting on this anti-Hillary Clinton campaign?"

Grassley, who at the time had a hold on roughly two dozen nominees to try to get answers from the State Department, repeatedly defended the committee's work.

"Looking out for the public interest isn’t a waste of time, and I’ll keep at it regardless of misguided attacks on my motivations or mischaracterizations of my work," he said at the time in response to Reid.