Rep. Paul D. Ryan led a parade of House Republicans Friday ripping into IRS Commissioner John Koskinen and the tax agency’s handling of emails related to the targeting of conservative groups.

The Wisconsin Republican told the former Clinton and Bush administration official, who was brought in last year by the White House to clean up the IRS, “Nobody believes you.”

Questions about the IRS and its handling of conservative groups during the early days of the Obama administration have ramped up dramatically in the past week, amid revelations the agency has irretrievably lost months of emails from Lois Lerner, the former IRS official at the center of the scandal.