Former White House chief strategist Stephen Bannon was tight-lipped during many of the questions asked by the House Intelligence Committee on Tuesday about the time he served in President Donald Trump’s administration.

Daily Beast reported Bannon informed the lawmakers that Trump has invoked the executive privilege for congressional inquiry purposes, citing it as the reason to for not answering many of the committee's questions.

Rep. Jim Himes (D-Conn.) called it, “a remarkably broad definition of executive privilege.”

This was the first time Bannon has testified before any of the committees probing into alleged Russian interference in the 2016 elections.

The New York Times reported the same day that Bannon was also subpoenaed by special counsel Robert Mueller last week to testify before a grand jury.

Daily Beast, in an exclusive Tuesday, reported executive privilege would not keep Bannon from revealing key information to Mueller and his team.

Talking about Bannon avoiding answering questions, Himes said on CNN, “So while we were able to ask and answer a lot of different kinds of questions, there were an awful lot of questions we weren’t able to answer based on this very novel theory of executive privilege . ”

He added Bannon’s attorney spoke to the White House, which indicated information while he was part of the Trump administration or Trump transition were off limits. Himes added an individual using executive privilege was not heard of and that this was essentially a “gag order.”

“This raises some very serious issues about whether we’ll get straight answers from anybody who is or was associated with the administration or is or was associated with the transition,” Himes said.

So, what is executive privilege and when is it essentially invoked?

Since the late 1700s, presidents have invoked the right of executive privilege to keep confidential information that might jeopardize the national security or might not be in the interests of the Executive Branch from being revealed.

The Constitution does not mention the term, neither does it explain this concept. But, presidents have long argued that it is implied in the “constitutionally mandated separation of powers,” National Public Radio said in a report.

The reason presidents have rallied behind this concept is because their aides would not be willing to give advice if there was a risk involved of them having to testify at some point in court or in front of a congressional committee.

The first president to invoke the executive privilege was George Washington in 1792, in order to keep information about an ill-fated expedition against American Indian tribes from the courts and Congress. Former President Dwight Eisenhower was the one who coined the phrase “executive privilege.”

Washington’s invoking the executive privilege did not help him as he had to hand over the information, but it did not stop other presidents from being successful.

Eisenhower used the concept to prevent the "provision of any data about internal conversations, meetings, or written communication among staffers, with no exception to topics or people," during the Army-McCarthy hearings of 1954, which were held to probe accusations between the army and the then United States Sen. Joseph McCarthy. Eisenhower, between 1955 and 1960, invoked the privilege 44 times.

Richard Nixon was one of the presidents who unsuccessfully invoked the executive privilege. He tried to withhold the White House audio recordings during the Watergate investigation, but failed to do so.

He wrote in his memoirs, “I was the first president to test the principle of executive privilege in the Supreme Court, and by testing it on such a weak ground, I probably ensured the defeat of my cause."

The United States v. Nixon was one of the defining moments for the concept. The then Supreme Court Chief Justice Warren Burger wrote “These are the considerations justifying a presumptive privilege for Presidential communications. The privilege is fundamental to the operation of Government and inextricably rooted in the separation of powers under the Constitution,” thus keeping the door open for other presidents to exercise the privilege.

During former President Barack Obama’s administration, the executive privilege was invoked to detain documents related to Operation Fast and Furious, which was designed to help the Bureau of Alcohol, Tobacco, Firearms and Explosives to crackdown on drug cartels in the U.S. and also to disrupt drug-trafficking routes.

It was also invoked during a lawsuit from the 2012 implementation of “Net Worth Sweep," a government plan to divert profits from Freddie Mac and Fannie Mae — two mortgage companies that were bailed out by taxpayers during the financial crisis — to the Treasury.