WASHINGTON - The House voted Thursday to make Attorney General Eric Holder the first sitting attorney general to be held in contempt of Congress for withholding documents requested as part of a congressional investigation into a botched gun-running operation.

On a 255-67 vote, the Republican-led House sanctioned Holder for failing to cooperate with an inquiry into Operation Fast and Furious, which was led by the Bureau of Alcohol, Tobacco, Firearms and Explosives from 2009 to 2011. On a separate vote, lawmakers voted 258 to 95 to approve a civil contempt charge against Holder.

Holder said the vote "is the regrettable culmination of what became a misguided -- and politically motivated -- investigation during an election year." Holder added that the Republicans leading the investigation "have focused on politics over public safety."

In the coming days, the House is expected to refer the criminal contempt charge to Ronald Machen, the U.S. attorney for the District of Columbia, to decide whether to press charges against Holder, his boss. Based on approval of the civil contempt charge, the House Oversight and Government Reform Committee is expected to mount a court challenge to President Obama's decision to invoke executive privilege over some of the documents sought by the panel.

'This is a somber day'

Before the vote, several Democrats walked off the House floor to protest what they characterize as a politically motivated investigation, backed in recent days by the National Rifle Association, to embarrass Holder and the White House. Led by House Minority Leader Nancy Pelosi, D-Calif., and House Minority Whip Steny Hoyer, D-Md., about 100 members left through the main center door of the House floor and then walked down the front steps of the U.S. Capitol.

"This is a somber day for the House," said Rep. Emmanuel Cleaver, D-Mo., chairman of the Congressional Black Caucus. "We are declaring, by walking out, we are not participating."

Hoyer then led the group in chanting, "Shame on you. Shame on you."

Pelosi said the vote "is not a principled effort to resolve the issue."

But House Speaker John Boehner, R-Ohio, disputed those charges.

"I don't take this matter lightly, and frankly hoped it would never come to this," he said from the floor. "The House is focused on jobs and the economy. But no Justice Department is above the law and no Justice Department is above the Constitution."

Although most Democrats left before the vote, 17 Democrats voted with Republicans. Most of the Democrats are moderates who have been endorsed in the past by the NRA, which said before the vote that it planned to track how members voted in determining future endorsements. Several moderate Democrats rely on the group's support in election years.

Over the course of an almost 18-month investigation, Republicans have said they are chiefly concerned with an attorney general whose Justice Department, in refusing to release documents, has covered up what senior officials knew about the operation that allowed thousands of firearms onto U.S. streets and into Mexico and resulted in the death of U.S. border agent Brian Terry in 2010.

At the heart of the matter

The conflict centers on a set of documents that the House Oversight and Government Reform Committee subpoenaed from the Justice Department in October as part of its investigation into Fast and Furious, during which the ATF lost track of most of the 2,000 weapons that they hoped to track later to a Mexican drug cartel.

A Justice Department official told lawmakers in a letter last year that the ATF had not ever "sanctioned" the effort. Ten months later, it acknowledged the botched operation -- which heightened suspicions among Republicans.

Justice officials have insisted that no senior officials in the department knew of the controversial tactics. They also have said they have worked hard to cooperate with requests from the oversight committee. During the past year, Justice officials have turned over 7,600 documents relating to the operation, as well as documents relating to another operation involving "gun-walking," as the tactic is known, during the George W. Bush administration.