The man who's just been forced out as acting chief of the IRS is apologizing for what he calls "the mistakes that we made and the poor service we provided."

Former Acting Commissioner of the Internal Revenue Service Steve Miller testifies during a hearing before the House Ways and Means Committee (Alex Wong/Getty Images)

Steven Miller has been testifying today to the House Ways and Means Committee about the IRS targeting of conservative groups, which got tougher scrutiny for their applications for tax-exempt status. Miller insisted that political bias wasn't the reason for the heightened scrutiny. Instead, he said, the IRS was struggling to efficiently handle growing numbers of applications for the tax-exempt status.

But Republicans on the panel made it clear they want IRS officials to pay a bigger price. Even though Miller and another top IRS official are stepping down, Republican committee chairman Dave Camp of Michigan said that wouldn't be enough. He said it's not a "personnel problem" -- but instead a problem of "the IRS being too large, too powerful, too intrusive and too abusive of honest, hardworking taxpayers."

He also said the activity seems to be a part of a broader pattern of intimidation and cover-ups by the Obama administration.

That brought a sharp retort from the committee's top Democrat, Sander Levin, who said the hearing shouldn't become a preview of next year's political campaigns.

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