What does the US Constitution actually say about impeachment?

House Judiciary moves forward with third ever impeachment effort against a US president, with Donald Trump in the cross-hairs

Light shines on the US Capitol dome in Washington, early Wednesday 4 December (AP)

This week, the House Judiciary Committee will take up the impeachment of Donald Trump, a continuation of the third-ever Congressional proceedings to potentially unseat a president of the US.

At the centre of the impeachment scandal are Mr Trump’s dealings with Ukraine, illustrated in a number of damning witness testimonies that corroborated a whistleblower complaint following a 25 July phone call between Mr Trump and Ukraine President Volodymyr Zelensky. During that call — as well as during a coordinated effort undertaken by a shadow diplomatic operation that bypassed normal State Department protocol — Mr Trump and his supporters apparently pressured the Ukrainian president to investigate the president's domestic political rival Joe Biden and the 2016 election.

Witnesses have now testified that the president was seeking a quid pro quo, and that he was using Congressionally allocated military aid to Ukraine and a potential White House visit as leverage.

On Wednesday, the Judiciary Committee will hear from three constitutional experts picked by Democrats, and another one picked by Republicans, as they seek to determine what exactly qualifies as an impeachable offence. Those experts include Noah Feldman of Harvard, Pamela Karlan of Stanford, Michael Gerhardt of the University of North Carolina, and Jonathan Turley of George Washington University.

Architects of the US Constitution established the concept of removing the president from office, through the authority of Congress, on grounds of “treason, bribery, and high crimes and misdemeanours”.

But definitions of those terms were not explicitly defined within the Constitution, appearing to give Congress a broad ability to interpret and determine impeachable offences.

Strictly speaking, the Constitution references impeachment in just four sections, as follows:

• In Article I, Section 2, Clause 5: "The House of Representatives ... shall have the sole Power of Impeachment."
• In Article I, Section 3, Clause 6 and 7: "The Senate shall have the sole Power to try all Impeachments. When sitting for that Purpose, they shall be on Oath or Affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no Person shall be convicted without the Concurrence of two-thirds of the Members present. Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honour, Trust or Profit under the United States; but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law."
• In Article II, Section 2: The president "shall have power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment."
• In Article II, Section 4: "The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors."

But what does all that mean? The president’s supporters have repeatedly argued that the abuses of power at the heart of the impeachment debate don’t constitute the so-called “high crimes and misdemeanours” that the framers had intended, and referenced in Article II, Section 4. So, let's take a look back at what that original debate entailed.

During the framers’ debates over charges considered grounds for impeachment during the Constitutional Convention in 1787, the authors determined that the phrasing of “treason and bribery” alone was not enough to encompass impeachable offences, and they settled on the inclusion of “high crimes and misdemeanours” to establish a broad definition that supplants ordinary criminality.

Alexander Hamilton, in his Federalist papers, had defined impeachment as a “method of national inquest into the conduct of public men” alleged to have violated the public trust,” adapting a concept introduced to the colonies from England, which established impeachment proceedings as early as the 14th century to hold royal advisers to public account.

Even at the time of the framers’ Constitutional Convention, Parliament was beginning the impeachment proceedings around British governor Warren Hastings, who was eventually acquitted.

The process begins with the House of Representatives. A member of Congress can introduce a resolution, or the House can agree to begin an investigation to determine the grounds for impeachment through an investigative or exploratory process led by the House Judiciary committee.

An impeachment trial can be approved by a simple majority vote.

In the House, roughly 227 Democrats and one independent from the 435-member Congress could be likely to support articles of impeachment.

If Congress votes to support articles of impeachment, or “impeaches”, the president will face the US Senate, which acts as the court for trial in the removal proceedings.

The chief justice of the US Supreme Court presides over that trial. In this case, that’s Chief John Roberts.

A group of Senate representatives called “managers” act as the trial’s prosecutors. A trial consists of evidentiary hearings, witness testimonials and examination.

The constitution says “the Senate shall have the sole Power to try all Impeachments … [but] no person shall be convicted without the Concurrence of two-thirds of the Members present.”

The 100-member Senate includes 53 Republicans, 45 Democrats and two independents, largely voting along Democrat lines. A two-thirds vote would require at least 20 Republicans to side with Democrats and independents to convict the president.

The Senate also notes that, in some cases, it could also disqualify officials found guilty from holding public offices in the future.

The Constitution also opens impeachment to the vice president and “all civil officers” in the US.

The House has initiated impeachment proceedings more than 60 times, but fewer than a third have moved to a trial.

From as early as 1799, the Senate has conducted 19 impeachment trials, including the impeachment attempts of two presidents — Andrew Johnson in 1868 and Bill Clinton in 1999. Neither was found guilty. (President Richard Nixon resigned from office in 1974 as Congress prepared to vote on his impeachment, which was nearly certain following the release of tapes linking his obstruction of justice and complicity in the Watergate scandal.)

Since 1789, about half of Senate impeachment trials have resulted in conviction and removal from office.

A successful conviction would result in the president’s removal of office — fines and potential jail time for crimes committed while in office would be determined in civil courts.