Russell George, the Treasury Department inspector general who wrote the audit on IRS targeting of conservatives that got so much attention, is returning to testify on Capitol Hill under oath later this week, at the request of Democrats. The House Oversight Committee — chaired by Rep. Darrell Issa — expanded its scheduled witness list to let Dems question George again about holes in his audit.

When George first testified about his audit findings back in May, it generated huge amounts of news media attention, and Republicans began openly insinuating that evidence would soon emerge that the White House — or “Washington” — orchestrated the targeting. Now, in a major turnabout, George will be answering questions about why key info that significantly muddies the “scandal” waters was not included in his audit.

George will face a raft of difficult questions about a number of new revelations. On Friday, Democrats on the Oversight Committee sent a letter to Issa highlighting new documents showing that George asked his top investigator to conduct a review of 5,500 emails from IRS employees, and that the investigator concluded the emails revealed “no indication that pulling these selected applications was politically motivated,” a fact the investigator termed “very important.” This was not included in George’s initial audit, Dems noted.

Furthermore, as Bloomberg reported, the new documents support a key assertion by Dems: that “anti-tax Tea Party groups received extra scrutiny because of confusion and unclear direction, rather than an attempt to hurt Republican leaning organizations.” Democrats want to ask George why the documents’ revelations were not included in the initial audit.

Separately, Dems on the Oversight Committee today released a memo noting that the committee has now interviewed 15 IRS employees (six who self-identified as Republicans or having voted for Republicans), none of whom “reported any political motivation or White House involvement.” Dems will likely point to this new evidence to ask George whether there is any support for the suggestion by top Republicans that the IRS targeting of conservatives was politically motivated.

All of this comes on top of revelations a couple weeks ago that “progressive” groups were also targeted on a “Be On The Lookout” list — a fact that was also missing from the initial audit. George responded in a letter that only six applications had the terms “progressive” or “progress” in them, and that a far greater percentage of Tea Party groups ended up being processed as political. But there are still outstanding questions about potential omissions and inconsistencies in George’s own response, which are detailed right here.

Among them: Were other political groups with liberal leanings that did not have “progress” or “progressive” in their names targeted, and how many of these groups are in the category of 202 groups vaguely marked “other” in the original IG audit saying they were originally signaled out as political?

George ‘s return to the Hill neatly encapsulates the ongoing collapse of the IRS story as the presidential scandal with Nixonian overtones Republicans initially proclaimed it to be. But will the Dem questioning of George — in which he’ll be pressed to account for the problems with the story that have emerged in recent days — get anywhere near the media attention the initial allegations did?

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.