A recent congressional oversight hearing on IRS targeting and harassment of conservative and Tea Party groups sparked several heated exchanges between members of Congress about the legitimacy of the official investigation of the scandal.

Much of the Feb. 5 hearing of the Subcommittee on Economic Growth, Job Creation and Regulatory Affairs focused on Barbara Bosserman, a major donor to President Obama and head of the joint Department of Justice and FBI investigation into IRS targeting of conservative and Tea Party groups.

Bosserman refused to appear before the committee to testify.

Rep. Matt Cartwright, D-Pa., disputed committee chairman Rep. Jim Jordan's assertion that Bosserman's involvement is a conflict of interest, citing legal experts who claim political donations are not relevant to case assignment and that it would be inappropriate for the DOJ to check a career prosecutor's political donations before assigning them to an investigation.

"To accuse her of being politically biased because she was exercising her right to participate in the democratic process of this nation is unacceptable," Cartwright said.

Jordan responded that Justice Department ethics rules say employees' participation in an investigation shouldn't create an appearance of a conflict of interest that would alter the public perception of the integrity of the investigation.

"You would think that Ms. Bosserman would look at this and say, 'You know what, maybe I should recuse myself and not head up an investigation,'" Jordan said.

Democratic members of the committee argued that Bosserman is only one member of a team of 13 working on the investigation, but Republicans on the panel said they believe Bosserman is in fact heading up the investigation, Jordan said.

Republicans on the panel were also critical of President Obama's Super Bowl Sunday interview with Fox News, in which he said that there isn't "a smidgen" of evidence of corruption in the IRS targeting.

"Thirteen people in six months have not had time to interview either of these two witnesses, and yet, the chief executive, the president of the United States, has already pre-judged the outcome of this investigation. So either it's ongoing or it's not," Rep. Trey Gowdy said.

"In either case, it is time for a special counsel," the South Carolina Republican said.

Witness Catherine Englelbrecht, president of the King Street Patriots and True the Vote, two of the groups targeted in the IRS scandal, told the committee she and her husband were the subjects of many personal and business audits and visits by several government agencies, including the Occupational Safety and Health Administration and the FBI.

Engelbrecht claimed that until she had applied for 501(c)(3) tax-exempt status for her organizations, she had never been audited.

She also told the committee that Rep. Elijah Cummings, D-Md., sent her three letters that expressed concerns about True the Vote and suggested that the organization needed to be investigated.

Cleta Mitchell, Engelbrecht's lawyer, said the letters "sought to delve into the inner workings of True the Vote and to make allegations about True the Vote that were not true. Demanding materials, demanding information, demanding that Catherine Engelbercht and representatives of True the Vote make themselves available in Washington. Frankly we think that is improper and we will deal with that in a different proceeding."

"We want to get to the bottom of how these coincidences happened," Mitchell said.

Cummings denied the allegations. In an unusual show of bipartisan support, Rep. Mark Meadows, R-N.C., yielded to Cummings, offering him the opportunity to give the witnesses personal assurances that he did not request the IRS investigation.

Mitchell was also involved in an unusual exchange with Cartwright, who questioned whether her firm represented progressive and liberal clients.

"As I say to people, in this law practice, you can't play for USC and Notre Dame," Mitchell responded.

Cartwright used Mitchell as an example of what he called serious concerns about the impartiality of the Republican majority of the committee.

"Sadly, only Tea Party groups are represented before this panel today," Cartwright said. "Since the identities of the witnesses has only been revealed on Monday afternoon, our staff was unable to identify a minority witness on such short notice and as a result, this is not a balanced hearing."

Jordan countered, saying committee Democrats knew about the hearing nine days before it convened.