WASHINGTON (AP) - The Treasury Department watchdog who detailed Internal Revenue Service mistreatment of tea party groups seeking tax-exempt status says he has no evidence the IRS also mishandled progressive groups' applications. In a letter obtained Thursday by The Associated Press, the inspector general for tax administration, J. Russell George, acknowledged that the term "Progressives" appeared on a list of terms used by IRS screeners from 2010 to 2012 to look for applicants with potential problems that would merit close scrutiny. But George said there was no evidence the IRS set aside progressive groups' applications because they appeared on that list. George said his investigators have "multiple sources of information corroborating," including interviews with IRS employees, emails and other documents, that tea party groups' applications were set aside for care examinations. But he added, "We found no indication in any of these other materials that "Progressives" was a term used to refer cases for scrutiny for political campaign intervention." George's letter, dated Wednesday, was sent to Rep. Sander Levin of Michigan, top Democrat on the House Ways and Means Committee. Levin is among Democrats who have complained that the report George released last month revealing IRS mistreatment of conservative groups unfairly focused on those groups and omitted mention of progressives. Democrats also have criticized George for not disclosing the inclusion of progressives even though lawmakers asked him about it at hearings. Levin wrote of "increasing evidence" that George's audit last month "was fundamentally flawed and that your handling of it has failed to meet the necessary test of objectivity and forthrightness." Some progressive groups seeking tax-exempt status have complained about facing lengthy delays and detailed questions from the IRS. It is unclear whether progressive groups faced the same extent of mistreatment as conservative organizations. Dozens of them ran into delays exceeding a year, and many received scores of detailed questions that officials have since said were overly intrusive, including demands for information about their donors. The back-and-forth came as the IRS' acting commission readied for questions from Congress for the first time since revelations that progressives joined the tea party on a list of groups whose applications for tax-exempt status drew extra scrutiny. Members of the House Ways and Means Committee planned to ask Danny Werfel about the report he issued Monday, six weeks after President Barack Obama named him to head the troubled agency. Werfel wrote that he found mismanagement but no purposeful wrongdoing at the IRS in a report that also pointed to the officials who have been replaced and other changes he has made. The committee chairman, Rep. Dave Camp, R-Mich., said Wednesday the report didn't answer key questions Republicans have had about the IRS' screening of conservative groups. Who started it? Why was it allowed to go on for so long? Why were conservative groups targeted for their political beliefs? Camp said. Democrats seem determined to shift the focus to this week's disclosure that the term "Progressive" was also on the agency's watch lists. IRS regulations allow tax-exempt social welfare organizations to engage in some political activity but it cannot be their primary mission. The agency must decide whether each applicant's activities meet those vague guidelines. The IRS has been under withering fire since May 10, when an agency official acknowledged that it had targeted conservative groups seeking tax-exempt designations for tough examinations. Until then, IRS officials had insisted that conservatives had not been singled out for such treatment. Some Republicans have suggested that the focus on conservative groups came from the White House or other Obama allies. There has been no evidence of that so far. Instead, according to investigators and testimony from IRS workers to congressional committees, workers in the agency's Cincinnati office that handled tax-exempt applications developed the lists to help them find groups that merited additional scrutiny. Obama and members of both parties in Congress have said such targeting is inexcusable. At least five top officials, including former acting Commissioner Steven Miller, have been removed.