The House of Representatives voted to impeach President Donald Trump on two counts; abuse of power and obstruction of Congress. It must now settle on a team of ‘impeachment managers’ to make the case against President Trump in a trial. The House is set transfer impeachment over to the Senate for said trial in the coming days.

The United States Senate has the power to try all impeachments and must do so under oath or affirmation. No person can be convicted without two thirds of the members present – notice the word ‘present’. In other words, only two thirds of the Senators present for the vote are required for conviction. Should 90 Senators be present, 60 votes would be enough. Assuming all 100 attend, it needs 67 – an unlikely outcome in this particular impeachment trial, as will be explained later.

The judicial branch of the federal government plays essentially no role in the impeachment process. But any trial requires a judge. Article I, Section III of the US Constitution stipulates that

When the President of the United States is tried, the Chief Justice shall preside.

And that is all. So what does that actually mean in practice?

The Chief Justice does not vote; he can neither acquit nor convict the president of the alleged high crimes and misdemeanours. The Senate must decide on and set the rules of the trial. The rules are voted on before the trial begins, and require a simple majority of 51 votes to take effect. During the impeachment trial, the Chief Justice rules on any motions that may arise. The most senior justice on the Supreme Court presides whilst the Chief Justice is away – in this case, Clarence Thomas, appointed in 1991 by George H.W. Bush. If the Chief Justice cannot attend or preside over the impeachment trial for whatever reason, it is unclear whether it can even take place; the constitution says he must.

The agreed upon Senate rules in the Bill Clinton impeachment trial, now precedent for future trials, set out just three criteria for the Chief Justice:

– To rule on all questions of evidence.

– To direct all forms of proceedings and …

– …all others not specifically provided for.

At the same time, the Senate’s long-standing rules say “the presiding officer shall have the power to make and issue” orders for conducting the trial, and may rule on all questions of evidence, including but not limited to, questions of relevance [and] materiality.

Proceedings ‘not specifically provided for’ is extremely vague. In all likelihood, it was designed as an insurance policy to have an impartial judge rule on unexpected or unforeseen circumstances that may arise during the trial. These Senate rules were passed by a vote of 100-0, after the majority and minority leaders, Tom Daschle (D-SD) and Trent Lott (R-MS), worked extensively together on the details, garnering support from their caucuses.

Then Chief Justice William Rehnquist viewed his role as ministerial and passive. Quoting the Gilbert and Sullivan operetta Iolanthe in 2001, he remarked ‘I did nothing in particular, and I did it very well’. Rehnquist ruled on a few objections. One came from Senator Tom Harkin (D-IA), where he noted that Senators’ role in the trial is as a court, not only as jurors. He refused to exclude evidence and place limitations on questions by House Managers. Rehnquist was strict on time during the Clinton debate. He gavelled down Senator Robert Byrd (D-WV), the chamber’s most senior Democrat, when he exceeded his limits giving a speech. Rehnquist also overruled the Senate majority leader on multiple occasions by keeping everyone in their seats into the early evening hours when they had asked to leave. Beyond that, Rehnquist always consulted the Senate parliamentarian. Impeachment is a political process, after all, not a legal one.

But that was then, this is now. The Senate is closely and sharply divided and the Chief Justice is John Roberts.

Roberts was appointed to succeed Rehnquist (whom he clerked for in the 1980s) by George W. Bush in 2005. Roberts is a lifelong Republican and conservative justice who joined the Reagan administration after clerking for Rehnquist. He won senators over by promising to be an umpire like judge who would calls ‘balls and strikes’ and not ‘pitch and bat’; not to make the rules but enforce them. It signalled he would not be an activist or ideological judge but a truly impartial and mediating presence.

Roberts has been a champion of restraint and long emphasised the independence of the judiciary from politics. At heart, he is an institutionalist who cares deeply that the American population trust the Supreme Court. His rebuke to Trump, who criticised a circuit judge as an ‘Obama judge’ ruling against his immigration plan, showed this.

In reality, however, Roberts’ rulings on the Court have advanced many conservative aims. These include gutting the Voting Rights Act, loosening campaign funding rules and restricting the power of unions. Then again, in 2012 he ruled to keep a core element of Obamacare in place, and last year struck down an attempt in Louisiana to close its last abortion clinics. Both angered many conservatives.

Presiding over the impeachment trial is likely not a role Roberts is looking forward to, as he will seek to not have the Court and its reputation dragged into the political muck. Following the impeachment trial, the Court is due to issue at least two politically toxic rulings that go straight to the centre of Trump’s presidential powers as the 2020 campaign sets off. The disputes revolve around key questions about executive authority, including whether Trump must answer to congressional subpoenas for his financial records and whether the president is immune from local and state criminal investigations. In short, the reputation of the Supreme Court as an independent, non-political branch of government is on the line in 2020.

With this in mind, Roberts will want to make the trial as bipartisan as possible. He will rule cautiously, prudentially and defer to the senators as much as possible. Republican senators privately hope this means deferring to the majority leader, Mitch McConnell (R-KY). Assuming similar rules to those in 1999 are adopted, Roberts can be expected to follow and apply these, although with some leeway. The Chief Justice retains the power to render his own decisions that can influence the trial’s trajectory. A majority of senators can always overrule him, though. Nevertheless, Roberts will attempt to come across as non-partisan and try not to sway the results one way or the other. Most importantly, he will want the process to look dignified amongst the day-to-day low-blow tactics coming from the White House.

The Chief Justice may break any logjams – but Roberts may not if it makes him seem partisan. Roberts will be neither sides’ saviour, though he will ensure order is maintained as the Senate sits quietly to hear the evidence. To this end, Roberts will also have a big say over the trial’s schedule. Like Rehnquist, he will probably hear cases on the Court in the mornings and attend the impeachment trial in the afternoons. This task might sound logistical but will have him stifling rambling senators, while forcing them to stay seated for long hours — senators cannot leave their seats.

It might not matter, anyway. Tribal partisanship in the Trump era is rife and the Republicans control the Senate with a 53-47 majority. McConnell has said he would not be a fair juror and is essentially doing as the White House wants. Many other senators on both sides of the aisle have indicated their minds are made up. The Senate can vote to adjourn the trial at any point with a simple majority, as well. President Clinton’s trial took about five weeks but the McConnell wants Trump’s to be as quick as possible. A small number of Republican defections to convict Trump are probable, but assuming all 47 Democrats voted to convict and remove Trump from office, it would be nowhere near the 20 senators that would be required.

Trump’s impeachment comes at a time tensions with Iran are boiling over. The Supreme Court is also set to rule on other high profile controversial topics in 2020. Three more among them are immigrant rights, LGBTQ+ employment rights and abortion. Impeachment is far more serious as it will test the endurance of the US political system in a time of crisis. If Roberts can preserve the institution of the Supreme Court, Americans can breathe a sigh of relief.