And so the Justice Department's complete reversal on Fast and Furious only stoked Republican suspicions of a cover-up.

Conservative bloggers and others suggested it was part of an administration back-door effort to impose new regulations on the sale of assault rifles and other "long-guns" - a contention that Democrats dismiss.

Indeed, the National Rifle Association in a statement supporting the vote to hold Holder in contempt of Congress accused the White House of using the Fast and Furious program to advance its gun control agenda.

The Republican leadership has worried that the Fast and Furious controversy could detract from election-year efforts to focus public attention on the ailing U.S. economy, and holding Obama responsible for it.

But Issa is aggressive and partisan. Last July 4, as downtown Washington was filling with tourists coming to see a nighttime fireworks display celebrating America's 235th birthday, Issa convened a private session in a Capitol Hill office to get testimony from ATF Acting Director Kenneth Melson.

That interview focused on wiretap requests ATF had sought for the straw purchasers and investigative reports related to Fast and Furious.

In it, Melson testified that he had discovered in March that ATF agents had been instructed to allow the guns to "walk" - meaning to flow unfettered, even if they went into Mexico. Investigators say Melson passed that information along to Justice officials. They want to know how far up the chain of command Melson's information went.

The White House executive privilege claim has put all post-February 4, 2011 documents off limits. Republicans argue they need those emails and other correspondence to corroborate Melson's testimony and determine who at Justice saw them.

Some also note that Holder was willing to turn over some "deliberative" documents before the committee resorted to a subpoena.

In a hearing before Issa's committee on February 2, 2012, Holder said the department had made "wholesale deliberative material available" on the February 4th letter. "I am not sure I know any Attorney General who has ever done that before to that degree, and I thought it was the appropriate thing, given the inaccuracies that were contained in that letter."

Democrats complain that Issa has shifted his focus from investigating how Fast and Furious went wrong to a look into how the Justice Department has communicated with Congress.

"The only reason they want these post February 4 documents is because they (Republicans) haven't gotten dirt on anyone at main Justice or the White House," a House Democratic aide said.

At the same time, Democrats argue, Issa and his fellow Republicans are turning a blind eye toward a similar "gun walking" operation that took place during the George W. Bush administration.

In its report accompanying the contempt resolution, Issa's panel said it wants to know who had information about and approved the tactics in Fast and Furious and whether high-level Obama appointees were involved.

"Documents that whistleblowers have provided to the committee indicate that those officials were the senior officials in the Justice Criminal Division, (Assistant Attorney General) Lanny Breuer and one of his top deputies, Jason Weinstein," the panel's report said.

Among the details Republicans think they might learn by looking at the post-February 4 documents are how much Breuer or Weinstein knew about Fast and Furious when they approved wiretaps of straw purchasers' telephones - or whether they failed to adequately read relevant documents before signing the wiretap applications.

That is another problem for officials at the Justice Department. Technically, at least, ranking department officials are by law supposed to review any wiretap requests. If they did not, they can be portrayed as careless stewards of the law, or worse. If they did, and if the requests included details of the operation, they have even more serious explaining ahead of them.

Democrats counter that any high-level Justice Department officials who may have approved those wiretaps used the same accepted procedures that other administrations have long employed. At that high level, they say, the details of a law enforcement operation are not being reviewed. That is the responsibility of officials on the scene.

(Editing by Fred Barbash; Desking by Vicki Allen)