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IRS headquarters, Washington, D.C. Reuters

A Senate hearing Tuesday morning on the Internal Revenue Service scandal could be the most acrimonious yet since such proceedings began last week, if not the most far-reaching. The Senate Finance Committee leadership on Monday sent a letter to the IRS requesting it turn over a broad range of communication on its heightened scrutiny of conservative groups between the last two election cycles.

Committee Chairman Sen. Max Baucus, D-Mont., and Ranking Member Orrin Hatch, R-Utah, want all documents of communication on the matter between IRS employees and White House staff, up to President Barack Obama.

Reports are that White House Counsel Kathryn Ruemmler was informed of the Treasury inspector general’s audit of the IRS as early as April 24. That’s more than two weeks before the report was released. According to The Associated Press, Ruemmler notified other senior staff, among them Denis McDonough, who serves as Obama’s chief of staff.

The White House says the president wasn’t aware of the IRS targeting of tea party groups until an official apologized on May 10 in advance of the report’s release less than a week later. Press Secretary Jay Carney has told the AP that Ruemmler was appropriate in not telling Obama of the audit and that no White House official interfered with it.

It wasn’t only the president who was kept in the dark. Based on the letter the committee sent to the IRS, it appears the agency failed to mention to lawmakers responsible for the nation’s revenue matters that it had inappropriately targeted conservative groups. When reports of the wrongdoing surfaced about two years ago, senators on the committee wrote then-IRS Commissioner Douglas Shulman, expressing concern.

The agency responded by giving a brief description of its procedures for processing tax-exemption applications, according to the letter. It didn’t mention subjecting the applicants to “intrusive and unwarranted scrutiny of their donor list and activities.”

“Targeting applicants for tax-exempt status using political labels threaten to undermine the public’s trust in the IRS,” the senators wrote. “Lack of candor in advising the Senate of this practice is equally troubling.”

The IRS has until May 31 to submit the information requested to the committee. Until then, here’s a preview of what to expect from Tuesday’s hearing:

Who Knew What And When?

This is the question that has been asked since the revelation that special scrutiny was applied to tea party and other conservative groups. In order to determine the facts for itself, the Finance Committee is requesting not only an explanation of how the IRS found out the improper practice was taking place. It also wants name, grade and title of agency supervisors, manager and officials who took part in, and approved the decision, and the actions they took after being informed. But the lawmakers aren’t stopping at agency heads. They want the same for all employees who gave the go signal to “be on the lookout” for political markers.

Was There Any White House Involvement?

There is currently no proven link to Obama or any White House officials from the IRS scandal beyond that the legal counsel was informed of the report. Rather than relying on news reports, committee members want every piece of communication -- text or video or otherwise -- that any IRS employees had with anyone in the White House or Treasury Department since February 2010. They also want the names and titles of all IRS officials who were aware the that anyone on the White House or Treasury Department had knowledge of the targeting.

What Kind Of Training Did IRS Employees Have?

Whether it is political bias or pure incompetence on the part of low-level employees in the Cincinnati office, lawmakers want to know. They have requested a description of the training provided to employees who are responsible for reviewing tax-exemption applications since Feb. 1, 2010, and all training materials.

What Internal Policies Were Violated Or Later Changed?

Lawmakers want the IRS to submit information about its existing policies -- and every single version of said policy between February 2010 and July 2012. Baucus and Hatch are trying to determine if employees in the Determinations Unit violated agency policy when they singled out certain nonprofits for higher scrutiny. They also want to know the discipline, if any, meted out to those employees and who they are.