The Justice Department moved Friday to shield Attorney General Eric Holder from prosecution after the House voted to hold him in contempt of Congress.

The contempt vote technically opened the door for the House to call on the U.S. attorney for the District of Columbia to bring the case before a grand jury. But because U.S. Attorney Ronald Machen works for Holder and because President Obama has already asserted executive privilege over the documents in question, some expected Holder's Justice Department to balk.

Deputy Attorney General James Cole confirmed in a letter to House Speaker John Boehner that the department in fact would not pursue prosecution. The attorney general's withholding of documents pertaining to Operation Fast and Furious, he wrote, "does not constitute a crime."

"Therefore the department will not bring the congressional contempt citation before a grand jury or take any other action to prosecute the attorney general," Cole wrote, in the letter obtained by Fox News.

A department official told Fox News the letter was "pro forma" -- or a formality -- considering that ex-Attorney General Michael Mukasey in 2008 also refused to refer two Bush White House aides to a grand jury after they were held in contempt.

Republicans nevertheless blasted the Justice Department for the move. Frederick Hill, spokesman for House Oversight and Government Reform Committee Chairman Darrell Issa, said "it is regrettable that the political leadership of the Justice Department is trying to intervene in an effort to prevent the U.S. attorney for the District of Columbia from making an independent decision about whether to prosecute this case."

Sen. Charles Grassley, R-Iowa, also wrote in a letter to Machen that the Cole letter "has put the cart before the horse." He suggested the U.S. attorney has not yet had a chance to make an informed decision on whether to move forward with the case.

The move by the Holder Justice Department, though, means Republicans are likely to take their case to civil court as they seek documents pertaining to Operation Fast and Furious -- which was already the unofficial plan. Along with the criminal contempt resolution, Republicans also passed a civil contempt measure Thursday allowing them to go to civil court to try and get an order that would compel the Obama administration to release the documents.

Issa, R-Calif., had acknowledged Thursday night that it was "very possible" the president would instruct the U.S. attorney not to prosecute Holder. He indicated Republicans would use the civil courts to get what they want.

"The House has authorized me to hire staff and legal staff who can pursue civilly through the courts to try to get a federal judge to order, separately, this discovery," he said.

Hill also told FoxNews.com that the next stop probably would be civil court, but he suggested the threat of criminal prosecution still looms. For now, the Obama administration can argue that its executive privilege claim over the documents protects Holder from the possibility of prosecution.

But if a civil court rules that claim invalid, Hill said, "then basically Justice has lost that shield."

If the administration still refused to turn over the documents the Republicans want, then they could start looking at prosecution more seriously.

Republicans technically have a handful of other options if the Justice Department still refused to take the case to a grand jury.

Republicans could move to appoint a special prosecutor or even move to impeach. The last time that happened with a Cabinet member, though, was in 1876 -- with the impeachment trial of war secretary William Belknap.

Hill said lawmakers are not looking at that option for Holder. They remain focused on the civil court route.

Machen and Holder also have spoken fondly of one another in public, further casting doubt on the possibility that the U.S. attorney would ever bring the case before a grand jury.

Machen is one of the two U.S. attorneys Holder tapped to lead an investigation into the recent rash of security leaks. In early June, Holder praised Machen and the other attorney as "great U.S. attorneys who have shown a willingness to take on difficult cases."

Meanwhile, Issa continued to add fuel to the debate over Fast and Furious when he entered into the Congressional Record a letter detailing a secret wiretap application pertaining to the operation.

In the letter, Issa claimed the affidavit contained "clear information that agents were willfully allowing known straw buyers to acquire firearms for drug cartels and failing to interdict them -- in some cases even allowing them to walk to Mexico."

Fox News' Mike Levine and FoxNews.com's Judson Berger contributed to this report.