WASHINGTON IS now sinking its teeth into a real scandal: the Internal Revenue Service (IRS) using ideological criteria to choose the targets of its attention. What we already know is bad enough. Given the seriousness of the charges and the unreliability of IRS disclosures so far, purposeful, sober investigation is exactly what is needed.

At first, the IRS’s admission that it flagged applications for tax-exempt status from tea party-type groups brought reaction that broke along partisan lines. But on Monday, President Obama called the news “outrageous,” adding: “I’ve got no patience with it. I will not tolerate it. And we will make sure that we find out exactly what happened on this.” Senate Majority Leader Harry M. Reid (Nev.) joined other Democratic lawmakers to support an investigation in his chamber, something Republican leaders in the House had pledged on Friday.

Any unequal application of the law based on ideological viewpoint is unpardonable — toxic to the legitimacy of the government’s vast law-enforcement authority.

A forthcoming Treasury Department inspector general’s report finds that IRS staffers looked for applications for tax-exempt status from groups that used in their names words such as “Tea Party,” “Patriots” and “9/12,” as well as ones that contained expressions of concern about government spending or criticism of how the country is run. One manager worried — with reason — that this targeting might result in “over-inclusion” of applications that needed no such scrutiny. By 2011, IRS staff had set aside more than 100 applications for added review. It wasn’t just a couple of wayward staffers involved but rather a number of IRS agents and managers.

The inspector general also reports that Lois Lerner, the head of the IRS’s tax-exempt organization office, knew about the targeting in 2011; she seemed to say Friday that she learned about it from news reports last year. That inconsistency raises suspicions about the agency’s statements that higher-ups didn’t know about the targeting and that there was no political motivation.

In fact, the portions of the inspector general’s analysis that circulated Monday raised many questions.

When Ms. Lerner heard about the targeting of tea party groups, she rightly demanded the practice end. But did she reinstitute checks against inappropriate targeting that had been in place years before? If not, why not? What are the safeguards now?

Who else knew about the targeting? In subsequent testimony, IRS leaders assured lawmakers that no one did. Were they ignorant or deliberately untruthful? Did they even ask before reporting to Congress?

Anecdotes about unreasonable demands for information are already circulating, but what were the practical effects of this policy on those 100-plus conservative applicants?

Considering that Ms. Lerner seems to have known about the targeting by 2011, did the IRS ever plan on revealing that it had singled out conservative groups? Or was it only the impending release of the inspector general’s report that compelled agency officials to ’fess up?

The administration should provide complete answers, and soon.