President Barack Obama plans to nominate James Comey, a former senior U.S. Justice Department official in the George W. Bush administration, to replace Robert S. Mueller III as FBI director, according to two people with knowledge of the selection process.

Comey, 52, was at the center of some of the most bruising debates over counterterrorism during the Bush administration and established a reputation as a fierce defender of the law and the integrity of the Justice Department regardless of the political pressures of the moment.

The expected nomination of Comey, a Republican, was seen in some quarters as a bipartisan move by a president besieged by Republicans in Congress. But Chuck Hagel's prior service as a Republican senator from Nebraska did not spare him from a bruising nomination battle for secretary of defense.