George, who wrote the report on the targeting, explained that his mission was to conduct an audit that would examine if wrongdoing occurred, rather than to necessarily identify who was responsible.
George said further examination of the case would take place, but he refused to provide any details.
Carney noted Monday that the inspector general's report found that there was no outside intervention regarding what he called "inappropriate scrutinizing of conservative groups" seeking tax-exempt status, and that no one in the White House intervened in the inspector general's review or "did anything that could be see as intervening."
In addition, Carney said, the misconduct had stopped in May 2012, almost a year before Ruemmler or anyone else at the White House was told of it by anyone at Treasury.
For his part, Miller denied deliberate discrimination for the targeting cited by the inspector general's report, calling the acts "foolish mistakes" made by overworked staffers struggling to enforce unclear regulations involving what political activity is permissible by tax-exempt groups.
"We are down a billion dollars over the last couple of years, the IRS is, and that's caused us to cut training in some areas," he said, adding that the agency deals with 70,000 applications for tax-exempt status. "Do we have the resources to get the job done. I don't believe we do at this point."
Democratic senators also focused on the ambiguity in the tax code and IRS regulations on the matter, saying the tax code needs to be altered. Republicans also called for tax code reforms, but with the goal of slashing the responsibilities of the agency as part of the party's longstanding push for smaller government and a reduced taxing authority.
IG blames a faulty policy
According to the inspector general's report, the IRS developed and followed a faulty policy to determine whether the applicants were engaged in political activities, which would disqualify the groups from receiving tax-exempt status.
The controversial move began in early 2010 and continued for more than 18 months, the report said, declaring that "the IRS used inappropriate criteria that identified for review Tea Party and other organizations applying for tax-exempt status based upon their names or policy positions instead of indications of potential political campaign intervention."
The conservative groups complain their requests were delayed for months or even years through the review process, which is intended to prevent ineligible political groups from getting tax-exempt status.
Miller told the House Ways and Means Committee on Friday that determining the political nature of groups was one of the hardest tasks of IRS officers responsible for assessing requests for tax exempt status.
The investigation by the Treasury inspector general for tax administration was initiated after congressional complaints began to surface in the media in 2012 that the IRS was targeting conservative groups and holding up applications.
In a written response included in the report, the IRS commissioner of the Tax Exempt and Government Entities Division said there was no criminal behavior behind the actions of the agents, but rather inefficient management.
Obama called practices described by the inspector general outrageous and forced Miller's resignation. In addition, the commissioner of the IRS Tax Exempt and Government Entities Division also announced his retirement Thursday. Joseph Grant will leave in June, according to an internal IRS memo provided to CNN. Miller also is scheduled to exit then.
Obama has appointed Danny Werfel, a White House budget office official who has served in both Democratic and Republican administrations, to succeed Miller through the end of the fiscal year on September 30.