What is executive privilege?

Executive privilege is the president's right to withhold information from Congress, courts or the public.

The legal principle allows the president and his closest officials to speak freely about sensitive issues such as national security without worrying about the discussions becoming public.

In theory, it makes the day-to-day work of the president and his aides more effective as they can provide the president with their unfiltered assessment of a situation. The Supreme Court said the principle, which is not explicitly mentioned in the US Constitution, is "fundamental to the operation of government and inextricably rooted in the separation of powers."

Read more: Trump: Mueller 'should not testify' before US Congress

When is it used?

Rarely. Trump's use of executive privilege on Wednesday to stop Congress from getting access to an unredacted copy of the Mueller report was the first time he had invoked the principle since his term began in January 2017.

Former Presidents George W. Bush, Bill Clinton and Barack Obama used executive privilege to block congressional investigations from accessing executive branch information.

Read more: Democrats file subpoena for full Mueller report

Are there any restrictions?

Yes. In 1974, the Supreme Court unanimously ruled that a president's right to privacy is not unlimited. Executive privilege must be weighed up against the right of Congress to oversee the work of the president.

Many legal experts interpret the ruling to mean that a president cannot try to cover up illegal acts by invoking executive privilege.

Executive privilege also cannot generally be claimed to prevent an investigation from accessing information that has already been shared with a third party.

Read more: Mueller report finds 'no collusion by any American,' says William Barr

Is Trump's executive privilege warranted?

Democratic Party lawmakers in the House of Representatives, the lower chamber of Congress, said Trump waived his right to use the principle because his aides discussed executive branch information with a third party: the Mueller investigation team.

Those revelations meant that the information was no longer private and was therefore no longer covered by executive privilege. Some legal experts and the Justice Department dispute that interpretation and argue the privilege still applies to the release of the unredacted Mueller report and other subpoenaed documents.

How does the attorney general fit in?

After Trump invoked executive privilege, the Democrat-led House Judiciary Committee voted in favor of holding Trump's top legal official, Attorney General William Barr, in contempt of Congress.

The move paves the way for a court battle between Trump and the Congress. A judge could force Barr to hand over the full Mueller report if they rule that executive privilege does not apply in this case.

amp/sms (Reuters, AP, dpa)

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