(Bloomberg) -- The battle between the Democrats who control the U.S. House of Representatives and the Republican who lives in the White House is a true power struggle. Congress has the power to demand testimony and documents and to hold accountable those who refuse to comply. President Donald Trump wields the power known as executive privilege to declare swaths of information off-limits to the legislative branch -- as he’s now done for Special Counsel Robert Mueller’s investigative documents. The clash between two co-equal branches of government is at the boundary of executive authority and congressional powers of oversight and impeachment.

1. Who does Congress get to question?

Anyone it needs to hear from to carry out its legislative functions -- almost. The Constitution did not spell out a power of investigation. But the British Parliament had long conducted inquiries as part of the process of developing legislation, and Congress quickly decided that it needed to do the same. The courts have upheld that power but set limits on it, most importantly the requirement that investigations relate to true legislative purposes. When the House or Senate believes it’s being wrongly rebuffed, it can vote to hold a person in contempt of Congress.

2. What is contempt of Congress?

It’s a misdemeanor defined in the U.S. federal legal code as when a witness summoned by Congress "to give testimony or to produce papers" refuses "to answer any question pertinent to the question under inquiry." Failure to comply is punishable by a fine of up to $1,000 "and imprisonment in a common jail" for up to one year. The House Judiciary Committee, under its Democratic chairman, Jerrold Nadler of New York, plans to hold U.S. Attorney General William Barr in contempt for not handing over a fully unredacted version of Special Counsel Robert Mueller’s report on Russian interference in the 2016 election and Trump’s possible obstruction of that probe. The committee also warned it could hold Donald F. McGahn II, the former White House counsel, in contempt if he doesn’t show up for a public hearing.

3. Could the attorney general really be sent to jail?

That’s highly unlikely. If House Democrats were to succeed in passing a resolution alleging contempt, normally the case would go to the U.S. attorney in Washington (or perhaps elsewhere) to pursue. All U.S. attorneys answer to the Justice Department -- the branch of government that Barr himself leads. Even if the case were then pursued in court, history suggests there would be a legal battle that could play out for years -- especially now that Trump has invoked executive privilege. Nadler hasn’t ruled out Democrats going as far as to assert Congress’s long-dormant “inherent contempt” powers by dispatching its sergeant-at-arms to arrest officials and then conduct a trial before the full House. The tactic, used early in Congress’s history, hasn’t been embraced since the mid-1930s. A recent federal court decision notes with understatement: “Exercise of Congress’s inherent contempt power through arrest and confinement of a senior executive official would provoke an unseemly constitutional confrontation that should be avoided.”

4. What is executive privilege?

It’s the limited right of the president to decline requests from Congress and the courts for information about internal White House talks and deliberations. The privilege is supposed to provide a safe space for presidents to get candid advice from aides without the concern that they’ll later be called to testify. Though U.S. presidents have claimed a right to confidentiality in the face of congressional demands virtually since the founding of the republic, the U.S. Supreme Court first recognized executive privilege in 1974 in the endgame to the Watergate scandal, when President Richard Nixon, claiming absolute protection of all presidential communications, tried to withhold audio tapes of Oval Office meetings and other evidence demanded by a special prosecutor. Even as it rejected Nixon’s specific argument, the court agreed that a president generally does have an interest in maintaining White House secrecy.

5. What determines the strength of a privilege claim?

Claims of executive privilege are strongest when they concern matters within the particular scope of the executive branch, such as national security, military affairs, law enforcement and foreign policy. In Nixon’s case, the court found that executive privilege can’t be used to hide potential evidence of a crime.

6. Where does impeachment fit in?

The U.S. Constitution says the president "shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors." The definition of "high crimes and misdemeanors" is largely up to Congress. Contempt of Congress was the grounds for one of the three articles of impeachment against Nixon approved by the House Judiciary Committee in 1974. (Nixon resigned when it became clear he would be impeached by the House and convicted by the Senate.) The leader of House Democrats, Speaker Nancy Pelosi, has said she opposes pushing for impeachment because it’s clear the required two-thirds of the Republican-majority Senate would never agree to remove Trump from office. But more recently she said that defying congressional subpoenas "could be part of an impeachable offense."

The Reference Shelf

©2019 Bloomberg L.P.