News sources are saying that Obama's Attorney General Eric Holder will resign as the nation's chief law enforcement officer today, ending nearly six years as AG.

Holder has been a thorn in pro-gun advocates sides for years, vowing to empower the ATF's mandate and put in place executive orders from the Obama White House imposing more restrictions on gun ownership and sales.

A senior Justice Department official tells ABC news:

"At a formal announcement later today, the attorney general plans to express his personal gratitude to the President for the opportunity to serve in his administration and to lead the Justice Department, which he will call the 'greatest honor of my professional life.' He will note he has loved the Justice Department since, when he was a boy, he watched how, under Attorney General Kennedy, the Department played a leadership role in advancing the civil rights movement. During his tenure as Attorney General, Holder has had Attorney General Kennedy’s portrait in his conference room."

Holder will reportedly stay in office until a replacement is found, and his resignation comes at a time when the Senate — which must confirm the next Attorney General — is tilting on the balance of a Republican majority.