U.S. Sen. Chuck Grassley — an Iowa Republican who has been a longtime advocate of whistleblower protections — is asking for more details behind President Donald Trump’s firing of the inspector general for the intelligence community who provided Congress with information the led to the president’s impeachment.

Michael Atkinson alerted Congress of a whistleblower complaint that involved President Trump’s communications with Ukraine’s president in what Democrats said was an illegal “quid pro quo” effort to uncover information about former Vice President and political rival Joe Biden.

The House impeached Trump in December on two charges but the Republican-led Senate acquitted him two months later.

Trump fired Atkinson late Friday, giving the House and Senate intelligence committees a required 30-day notice of his removal. Atkinson was placed on administrative leave, which means his tenure effectively ended Friday.

Inspectors general play a critical role in protecting against fraud, waste, abuse and misconduct, serving “as an outlet to whistleblowers who shine a light to problems in government,” Grassley said in a statement Saturday.

“They help drain the swamp, so any removal demands an explanation,” Grassley said. “Congress has been crystal clear that written reasons must be given when IGs are removed for a lack of confidence. More details are needed from the administration.”

Jason Clayworth is an investigative reporter at the Des Moines Register. He can be reached at 515-699-7058 or jclayworth@dmreg.com