It's actually unusual that he stayed this long:

Eric Holder Jr., the nation's first black U.S. attorney general, is preparing to announce his resignation Thursday after a tumultuous tenure marked by civil rights advances, national security threats, reforms to the criminal justice system and 5 1/2 years of fights with Republicans in Congress.

Two sources familiar with the decision tell NPR that Holder, 63, intends to leave the Justice Department as soon as his successor is confirmed, a process that could run through 2014 and even into next year. A former U.S. government official says Holder has been increasingly "adamant" about his desire to leave soon for fear that he otherwise could be locked in to stay for much of the rest of President Obama's second term.

Holder already is one of the longest-serving members of the Obama Cabinet and ranks as the fourth-longest tenured AG in history. Hundreds of employees waited in lines, stacked three rows deep, for his return in early February 2009 to the Justice Department, where he previously worked as a young corruption prosecutor and as deputy attorney general — the second in command — during the Clinton administration.

But some of that early glow faded in part due to the politicized nature of the job and in part because of Holder's own rhetoric, such as a 2009 Black History Month speech where he said the country was "a nation of cowards" when it comes to discussions about racial tension.

Five years later, violence erupted between police and protesters in Ferguson, Mo., after a white policeman killed an unarmed black 18-year-old. And this time, the White House dispatched Holder to speak his piece, in effect jump-starting that conversation and helping to settle nerves in the frayed community.