Dianne Feinstein, chair of the Senate Select Committee on Intelligence, has repeatedly defended the National Security Agency's vast collection of Americans' private email and phone records. So when the California Democrat went to the Senate floor Tuesday to allege that the CIA had "violated the separation of powers" by spying on her panel, some observers detected a self-serving inconsistency in her outrage over government snooping.

But if, as Sen. Feinstein charged, the CIA secretly took committee documents, searched its computers and tried to intimidate its investigators, what she called her "grave concerns" are justified.

As Sen. Lindsey Graham, R-S.C., aptly put it Tuesday, if Sen. Feinstein's charges are valid, "this is Richard Nixon stuff."

CIA Director John Brennan quickly urged lawmakers not to rush to judgment against his agency. He also suggested that wrongdoing in this controversy might have been committed not by the CIA but by intelligence committee staffers.

Citing investigations by the CIA inspector general and Justice Department, Mr. Brennan said: "Appropriate authorities right now, both inside of CIA as well as outside of CIA, are looking at what CIA officers as well as [intelligence committee] staff members did."

Early this year, the CIA filed a criminal complaint asserting that Senate committee staffers had illegally taken some of the agency's computer records regarding the "enhanced interrogation" methods it has used on terror suspects.

Certainly some members of the Senate committee and the CIA have been at odds over whether those techniques could fairly be described as "torture." And CIA officials have insisted that information leaked by the panel grossly distorted those efforts to obtain life-saving information from terror detainees - and the results they achieved.

Yet you don't have to oppose the use of waterboarding and other controversial interrogation tactics on terror suspects to oppose CIA spying on federal lawmakers.

And Sen. Feinstein can't fairly be dismissed as a knee-jerk critic of the CIA. For instance, she has repeatedly backed the agency's drone strikes against terror suspects in Afghanistan and elsewhere.

So when she contends that the CIA has defied Congress' proper oversight of the agency, that must be taken very seriously.

As for Mr. Brennan's prediction that "a lot of people who are claiming that there has been this tremendous sort of spying and monitoring and hacking will be proved wrong," he should know that any sort of CIA "spying and monitoring and hacking" of a congressional committee is intolerable.

And beyond that obvious constitutional concern lies this practical one: Considering the numerous international menaces America faces, including Islamic radical terrorism, nuclear-armed North Korea, nuclear-arms-seeking Iran, Russian aggression in Ukraine, China's provocative moves in Asia, and ongoing Mideast turmoil that includes a brutal civil war in Syria, the CIA has much more valid things to do than spying on federal lawmakers.

If Sen. Feinstein's allegations are incorrect, she should apologize.

But if she's proven right, stern measures must be taken to assure that CIA officials understand what their proper job is - and what it isn't.