Contempt citation

In June Mr Holder became the first sitting attorney general to be held in contempt of Congress. He faced proceedings after the House Oversight Committee led its own investigation into operation.

The roots of that investigation began on 4 February 2011 when the justice department sent lawmakers a letter denying it had sanctioned or otherwise knew about guns illegally ending up Mexico.

The department withdrew the letter 10 months later, acknowledging the operation had allowed guns across the border.

Led by Republican Darrell Issa, the House Oversight Committee subpoenaed documents for that 10-month period.