Mr Durham noted that Mrs Clinton and others had received "defensive briefings" from the FBI aimed at "those who may be the targets of nefarious activities by foreign powers". Mr Trump had not.
"The Department [of Justice] and the FBI failed to uphold their important mission of strict fidelity to the law," the report concluded.
In a statement, the FBI said it had "already implemented dozens of corrective actions".
"Had those reforms been in place in 2016, the missteps identified in the report could have been prevented," the statement added.