House Republicans are pressing forward with their contempt of Congress civil case over Operation Fast and Furious despite the release of a book-length investigative report that lawmakers on both sides of the aisle praised as comprehensive.

"We have no choice," Rep. Darrell Issa, R-Calif., said on Fox News when asked about pursuing the court case.

The chairman of the House Oversight and Government Reform Committee explained that the contempt of Congress vote against Attorney General Eric Holder earlier this year essentially "ordered" lawmakers to go to court to attempt to pry loose from the Obama administration documents they have withheld.

An Issa spokesman also cited an IG finding that the department responses to Congress were "troubling." "This finding only enhances the importance of compelling the production of wrongly withheld documents," the aide said.

Beyond that, Republicans argue that the nearly 500-page inspector general's report doesn't erase the need to take a stand against what they see as an inappropriate claim of executive privilege by the administration.

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Sen. Charles Grassley, R-Iowa, who said he "absolutely" backs pursuing the court case, claimed Congress needs to see the documents to "get to the bottom of this."

"If the president of the United States gets away with 74,000 pages of executive privilege ... you can see what an abuse of executive authority and executive privilege that is, and we can't let that happen," he told Fox News.

A major target for Republicans is a set of documents supposedly relating to a February 2011 letter to Congress that falsely claimed the ATF was unaware the operation involved the underground sale of assault weapons. The Justice Department's inspector general report faulted officials for relying on inaccurate information in drafting that letter.

Republicans want to know more. But Democrats have nudged them to drop the case.

Rep. Elijah Cummings, D-Md., the top Democrat on the House oversight panel, said Thursday that after a year-and-a-half investigation by the IG that reviewed 100,000 documents, Republicans should resolve the "remnants of this dispute" without much ado.

"I note that the administration did not assert executive privilege over any part of the inspector general's report, over any of the documents relied on by the inspector general. In fact, the department went a step further yesterday: It sent to this committee more than 300 pages of additional documents that were withheld previously," Cummings said. "I urge the committee to reconsider its position and settle the remnants of this dispute without resorting to unnecessary and costly litigation that nobody in this country wants."

One Justice official resigned and another retired in the wake of the IG report. The report faulted a range of federal agencies for the failed anti-gunrunning program and accused officials in charge of a "disregard" for public safety.