Lois Lerner, head of the IRS unit that decides whether to grant tax-exempt status to groups, leaves after being dismissed from a House Oversight and Government Reform Committee hearing on Wednesday. J. Scott Applewhite/AP hide caption

itoggle caption J. Scott Applewhite/AP

The John Weld Peck Federal Building in Cincinnati, where many of the missteps by IRS workers who targeted conservative groups occurred. Al Behrman/AP hide caption

itoggle caption Al Behrman/AP

The controversies facing his administration could be creating a stiff headwind for President Obama's second-term agenda. Jack Plunkett/AP hide caption

itoggle caption Jack Plunkett/AP

An Internal Revenue Service official apologized for workers who targeted certain conservative groups. But that did little to defuse the situation. Susan Walsh/AP hide caption

itoggle caption Susan Walsh/AP