Jeff Sessions could invoke 'executive privilege' during his testimony Tuesday - here's what that means

Attorney General Jeff Sessions is set to testify before an open session of the Senate Intelligence Committee Tuesday afternoon, and speculation is mounting over whether he will invoke something called "executive privilege" to avoid answering certain questions.

The idea is that the executive branch has the right to have internal conversations that remain private for national security reasons, or to ensure government functions properly.

The White House so far has not clarified whether Sessions will make such an invocation during his testimony, but Press Secretary Sean Spicer told reporters on Monday that it "depends on the scope of the questions."

"To get to a hypothetical at this point would be premature," Spicer said.

The issue of executive privilege also surfaced prior to former FBI Director James Comey's hearing last week, culminating in a White House announcement that Trump would not seek to prevent Comey from testifying. Nonetheless, Spicer said in a statement that "the president's power to assert executive privilege is well established."

What is executive privilege?

Executive privilege can be claimed by the president or members of the executive branch to withhold certain information from the courts and Congress, including information that has been subpoenaed.

Executive privilege is a hazy concept, as it is not explicitly mandated or even mentioned in the US Constitution. Presidents have frequently argued, however, that the privilege is part of the Constitution's separation of powers principle, and is necessary to ensure that aides and officials feel they can speak openly on policy options and decisions.

The Supreme Court has also ruled that communications that take place within a president's administration are protected under a "presumptive privilege," which is "fundamental to the operation of government and inextricably rooted in the separation of powers under the Constitution."

When has it been used in the past?

The Trump administration would be far from the first to invoke executive privilege - although previous presidents have had mixed success in asserting that power.

Executive privilege has been invoked, in some form, by presidents dating back to George Washington, who in 1792 was unwilling, but eventually compelled to hand over information regarding a failed expedition against Native Americans. It wasn't until President Dwight Eisenhower that the term "executive privilege" was coined, however.

Other presidents to famously claim the privilege include Thomas Jefferson, Richard Nixon, Bill Clinton, George W. Bush, and Barack Obama.

Nixon was particularly notorious for his use of executive privilege during the Watergate investigation, which ended in a Supreme Court decision that found executive privilege to be constitutional and sometimes necessary, but not an absolute power. The court then compelled the Nixon administration to turn over the Watergate tapes to the special prosecutor. Shortly after, Nixon resigned.

What will happen if Sessions invokes executive privilege?

Sessions would likely face criticism from the Senators questioning him - particularly the Democrats - should he refuse to answer certain questions.

The Senate Intelligence Committee expressed frustration last week with top intelligence officials when they refused to say whether Trump had asked them to interfere with the FBI's Russia investigation, though they did not explicitly cite executive privilege.

It's also possible that the Senate Intelligence Committee could seek to get certain questions answered in a closed session or hold Sessions in contempt, according to legal experts. But the latter option is unlikely as it would prolong the testimony and launch a contentious court battle.

"If they choose to do so, that could lead to litigation in court about whether the privilege exists and whether it applies in the instance that he invoked it," Diane Marie Amann, a University of Georgia law professor, told CNN.