Witnesses at a congressional oversight hearing Wednesday questioned the Justice Department's decision to appoint Obama donor Barbara Bosserman to the investigation into IRS targeting of conservative nonprofit groups.

The House Committee on Oversight and Government Reform's subcommittee for economic growth, job creation and regulatory affairs continued its probe into IRS targeting with its second hearing in three weeks.

Bosserman's appointment sparked a heated discussion between members about the relevance of her donor status at the last hearing on Feb. 6.

Richard Painter, former chief ethics lawyer to President George W. Bush, said no rule specifically prohibits a prosecutor who has made campaign contributions from involvement in an investigation.

But Painter said he believes the investigation has been compromised by the controversy over Bosserman's appointment.

"If I had been a senior official at the DOJ, I would've chosen, in this instance, to choose someone to lead the investigation who did not have a strong affiliation with either of the two major political parties," Painter said.

Glenn F. Ivey, former assistant U.S. attorney, raised concerns about a "chilling effect" if Bosserman were to be removed from the investigation.

"Maybe if you had a do-over again, you wouldn't put her in place, but now that she's there, if you remove her, you really do send a message to all the other prosecutors out there that if you've given contributions, you'd better stop and if you've been thinking about doing it, you'd better stop," Ivey said.

Other witnesses disagreed and said that they had removed prosecutors from cases in similar situations in the past.

"The reason you would do that, and the reason it's not only proper and not only an exercise of good judgement but is required, because there's a duty of avoiding even the appearance of impropriety," said George Terwilliger, former deputy attorney general under Bush.

Rep. Jim Jordan, the Ohio Republican who is chairman of the subcommittee, cited DOJ ethics rules as why Bosserman should recuse herself from the investigation to avoid an appearance of a conflict of interest.

Rep. Matt Cartwright, D-Pa., said Bosserman is only one of 13 investigators assigned to the case and that the DOJ has never confirmed whether she is leading the investigation.

Cartwright chastised the committee, saying responding to the congressional investigation has cost the IRS $14 million so far.

According to Cartwright, the subcommittee has interviewed 38 IRS and Treasury employees and received more than 385,000 pages of documents.

"This is the exact same thing that some of the groups that are applying for their (c)4 status at the heart of this matter are complaining about, that they are being scrutinized excessively because of their political stances and their involvement in the political process," Cartwright said.

"I would just remind the ranking member that no one's talking about Ms. Bosserman not keeping her job. No one's ever questioned the character or professionalism of Ms. Bosserman," Jordan responded.