As they questioned Attorney General Jeff Sessions about Trump associates' contacts with Russian agents this week, senators asked him eight times whether he was invoking executive privilege in refusing to answer questions.

And eight times, Sessions walked a fine line. "I'm not claiming executive privilege, because that's the president's power, and I have no power to claim executive privilege," he said.

But he added, "There are also other privileges that could be invoked."

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Coming just five months into the Trump administration, Session's refusal to answer questions — without exerting executive privilege — could set the stage for high-stakes battles in the investigation over Russian tampering with the 2016 presidential election.

But it's also just the latest performance of the awkwardly choreographed dance between the presidents and Congress over exerting the president's constitutional right to withhold information.

"What he did was an extreme version of that we've seen for years, which is presidents who want the advantages of executive privilege but don't want the political and legal baggage that comes with it," said Heidi Kitrosser, a law professor at the University of Minnesota and author of Reclaiming Accountability: Transparency, Executive Power and the U.S. Constitution.

The Trump White House, she said, seems to want it both ways. "Either you exert executive privilege or you don't," she said.

Battles over executive privilege date back to the George Washington administration, but reached a crescendo when President Richard Nixon refused to turn over tapes of his White House conversations. (The Supreme Court unanimously ruled against Nixon, who resigned two weeks later.)

Since then, presidents have increasingly taken to "invoking executive privilege without using the words," said Mark Rozell, dean of the George Mason University public policy school. That makes it difficult to determine how many times presidents actually invoke it.

"The trouble is that some presidents have exercised this power numerous times without using the label," said Rozell, author of Executive Privilege: Presidential Power, Secrecy and Accountability. "With all these word games, it's hard to get a reliable count. And a count of formal claims would miss all the actions that should have resulted in formal claims."

Among the questions Sessions refused to answer based on the privilege:

► Whether Trump had discussed the possibility of pardons for anyone involved in the Russian matter;

► Whether Trump had expressed frustration at Sessions for recusing himself from the investigation; and

► Whether Trump had cited the Russian probe in his decision to fire FBI Director James Comey.

Rozell said Sessions was playing it loose when he refused to answer those questions, which he should have anticipated before the hearing.

But the Justice Department said Sessions' testimony was not out of the ordinary.

A 1982 memo from President Ronald Reagan directed that only the president can invoke executive privilege, and that administration officials should ask Congress to hold their requests for information in abeyance while they consult the White House. "The purpose of this request is to protect the privilege pending a presidential decision," the memo said, and "does not constitute a claim of privilege."

"This was a voluntary appearance at a hearing," said Justice Department spokesman Ian Prior. "The attorney general was well within the longstanding practice outlined by the Reagan memo of protecting potentially privileged information from disclosure while the department engages in the normal process of working to accommodate congressional requests in an effort to minimize the need for invoking executive privilege."

That means Sessions may yet have to answer those questions — or stand behind executive privilege.

"There were several questions that you chose not to answer because of confidentiality with the president," Senate Intelligence Committee Chairman Richard Burr told him Tuesday. He asked Sessions to go back to the White House and sort out which questions he could answer, and "provide those answers in writing to the committee."