United States Attorney General Eric Holder holds a news conference announcing updates in the Justice Department’s investigation of the shooting of Michael Brown in Ferguson, Missouri, in Washington September 4.

WASHINGTON — U.S. Attorney General Eric Holder, an unapologetic liberal voice and one of President Obama’s closest allies, announced he is stepping down after a term marked by advances in civil rights and frequent battles with Republicans in Congress.

Holder’s departure after nearly six years sets up a potentially tense confirmation battle with Republicans in a lame-duck U.S. Senate session scheduled after the Nov. 4 midterm elections, when Republicans hope to capture a Senate majority that would take office in January.

A White House official said Obama has not made a decision on a replacement and will not name a successor this week. 

Holder had previously signaled his plans to step down by the end of the year, and the Justice Department said he finalized his decision at a White House meeting earlier this month.

Holder was a natural choice for attorney general after campaigning for Obama in 2008, when he took on the sensitive job of helping to vet Obama’s choices for a vice presidential nominee.