Thousands of documents sought by congressional investigators about a disastrous plan by federal agents to allow guns to "walk" into the hands of Mexico's drug cartels will now be out of reach. The Obama administration has asserted its executive privilege to withhold the documents – just as lawmakers prepare to vote to hold the nation's top lawman in contempt of Congress.

In other words, the political battle between the White House and Capitol Hill over the scandal could be on the verge of going nuclear.

For a year and a half, investigators in Congress have pressed Attorney General Eric Holder to provide tens of thousands of documents about Fast and Furious. At first one of several sting operations by the ATF's Phoenix Field Division against the cartels, the operation ended in disaster as hundreds of guns were allowed to move freely into Mexico, many becoming lost until turning up at murder scenes and cartel stockpiles. Included in this list of smuggled guns were AK-47 variant rifles discovered in Arizona at the scene of a shootout between bandits and Border Patrol tactical officers. The Dec. 14, 2010, firefight caused the death of Border Patrol agent Brian Terry.

Tens of thousands of documents related to the operation could reveal which officials knew what, and when. That is, if those documents ever saw the light of day. Republicans on the House Oversight and Government Reform Committee have accused Holder of stonewalling investigators, and issued a (unsuccessful) subpoena in October demanding the documents. A meeting last night between Holder and Rep. Darrell Issa, the chairman of the committee, ended without a compromise being reached. If today, a majority of committee members vote to hold Holder in contempt for not abiding by the subpoena, a resolution will then have to move to the House Floor. But because of executive privilege, Holder is no longer required to abide by the subpoena at all.

Though without executive privilege, Holder could face up to a year in prison and a fine of up to $1,000. Though, that's only theoretical. If Holder is held in contempt by the committee, it will be among only a few attempts in decades against an executive branch official. But no contempt action of the sort has been prosecuted in decades except once.

Contempt actions were used against Henry Kissinger in 1975, Interior Secretary James Watt in 1982 and Attorney General Janet Reno in 1998. Each official was held in contempt by committees but compromises were reached before a contempt action ever reached a full House vote. Anne Gorsuch Burford, then-administrator of the Environmental Protection Agency, was held in contempt in 1982 by the full House, but was never prosecuted. Karl Rove and Harriet Myers were held in contempt in 2008, but neither actions were ever resolved. EPA official Rita Lavelle was held in contempt, prosecuted and convicted of lying to Congress in 1983.

During testimony in February, Holder said the Justice Department has provided "virtually unprecedented access" (.pdf) through (limited and redacted) internal documents. "This has been a significant undertaking for Department employees — and our efforts in this regard remain ongoing," he said. Though, Holder also said the documents included evidence "some of the information [the Justice Department] provided was inaccurate" — including a letter sent to Sen. Charles Grassley of Iowa one year ago denying that Fast and Furious ever took place.

The Justice Department has also maintained that 7,600 documents have already been turned over, and that releasing more documents could harm ongoing investigations.

Fast and Furious was also not the first ATF operation to run guns. A report released in January by House Democrats described the plot as "the latest in a series of fatally flawed operations run by ATF agents in Phoenix and the Arizona US Attorney’s Office," beginning in 2006 with another shuttered plan called Operation Wide Receiver. In the beginning, Phoenix-based ATF agents "went forward with plans to observe or facilitate hundreds of suspected straw firearm purchases," according to the report.

The ATF’s history of running guns down to Mexico prior to Fast and Furious could be one of Holder’s main defenses. If the ATF — specifically, ATF agents in Phoenix — were letting guns walk two years before Holder was appointed Attorney General, then the reasoning is that ATF agents likely proceeded at their own discretion. Though, if documents are released that reveal that the upper tiers of the Justice Department – including Holder – knew about the plan (or plans) all along, then Holder may be forced to resign.

With Obama's asserting executive privilege, however, that's become a lot less likely.

UPDATED: The House Committee on Oversight and Government Reform has voted to hold Holder in contempt. Next, the committee will send a contempt citation to the House for a full vote. The vote was (predictably) along partisan lines, with 23 in favor to 17 opposed. Though, it's worth noting that the House doesn't have to vote on it. According to the Associated Press (via NPR), the more likely scenario is that the contempt citation will be used as a bargaining chip during negotiations.