THE BURNED OVER DISTRICT

As is natural in Washington, the big money groups escaped an serious oversight, even in the face of outside complaints about their activities.

During the same period, the agency singled out dozens of Tea Party-inspired groups that had applied for I.R.S. recognition, officials acknowledged on Friday, subjecting them to rounds of detailed questioning about their political activities. None of those groups were big spenders on political advertising; most were local Tea Party organizations with shoestring budgets.

For the I.R.S.’s bipartisan legion of critics, the agency’s record has underscored its contradictory and seemingly confused response to the fastest-growing corner in the world of unlimited political spending: tax-exempt groups that have paid for at least half a billion dollars in campaign ads during the last two election cycles.

The I.R.S. has done little to regulate a flood of political spending by larger groups — like Crossroads Grassroots Policy Strategies, co-founded by Mr. Rove, and Priorities USA, with close ties to President Obama — as well as Republican leaders in Congress and other elected officials. And an agency that is supposed to stay as far away from partisan politics as possible has been left in charge — almost by accident — of regulating a huge amount of election spending.

“We’ve complained about a few big fish and we’ve heard nothing from the I.R.S.,” said Paul S. Ryan, senior counsel at the Campaign Legal Center, which filed many of the complaints with the agency. “We would far rather see scrutiny of these big fish — the groups that spent hundreds of millions of dollars to influence elections — than to see the resources spent on hundreds of small groups that appeared to spend very little on elections.”

Almost all of the groups in question are organized under 501(c)(4) of the tax code, which regulates nonprofit groups engaged in promoting “social welfare.” At least 16 such organizations spent a million dollars or more on campaign advertising in the 2012 elections. (Crossroads GPS and Priorities USA also run “super PACs” with similar names that spent millions more.)

I suppose if the IRS ever tried to go after the big fish, Weepy John's House caucus would try to totally defund the IRS faster than you can say "repeal Obamacare".