It is an unfortunate fact that several of the successful, and worst, terrorist attacks in this country (USA) have been carried out by right wing extremist groups or "lone nutcases" closely associated with Tea Party causes.
During the Obama administration right wing hate radio, and television, have blatantly espoused the overthrow of the government, advocated the failure of both foreign and domestic policies, and have made thinly veiled threats to assassinate prominent "liberal" political figures, including the president.
Given these right wing and Tea Party agenda, it makes perfect sense that the IRS, which was mandated to target terrorist affiliated organizations, would target Tea Party groups, and it is mind boggling that they would apologize for doing so.