The US Senate on Tuesday will start former President Donald Trump's historic second impeachment trial. He faces a single charge of inciting the deadly US Capitol attack on January 6.

An impeachment conviction requires a two-thirds majority in the evenly split, 100-member Senate. This means that 17 Republicans would need to join the Senate's 50 Democrats in that decision.

Why is Trump on trial?

The charge of "incitement of insurrection" that was passed by the Democratic-led House of Representatives on January 13 focused on Trump's speech to a crowd of supporters shortly before thousands stormed the Capitol a week before. 

At a rally in Washington on January 6, Trump repeated claims of election fraud, telling his followers: "We fight like hell. And if you don't fight like hell, you're not going to have a country anymore."

Shortly after the speech, hundreds of Trump supporters surrounded and then stormed the US Capitol, where Congress was formally certifying Democrat Joe Biden's election victory.

The violent attack left five people dead including a Capitol Police officer. Over 100 other Capitol officers sustained various injuries ranging from permanent blinding and broken bones to cuts, bruises and trauma.

What is the trial's likely schedule?

Both Democrat and Republican lawmakers are hoping for a swift trial lasting approximately one week.

On Tuesday, senators will be allowed four hours to debate the constitutionality of the article of impeachment against Trump — in particular, whether it is possible to try a former president.

They will vote on the constitutionality issue on Tuesday. Should the dismissal motion pass, the trial would end at this point.

If the motion once again fails, then beginning on Wednesday, each side will have up to 16 hours to lay out their respective cases, spread out over two days per side.

During this time, the House managers and Trump's defense lawyers will present their arguments directly to the senators and then face questions.

Subpoenas for testimony may be issued, witnesses could be called and more evidence might be requested. Though asked, Trump has declined to testify in his defense.

After a brief pause, the trial will likely resume Sunday. Both sides will have two hours to present closing arguments. 

If the Senate deadlocks 50-50 at any point, which is possible given the even split between parties, then Vice President Kamala Harris will be asked to vote as a tie-breaker. Though this could happen during procedural votes, Harris will not be voting on any final impeachment deliberations.

What is Trump's expected defense?

Trump's lawyers have blasted the impeachment case against him as an act of "political theater." They accuse House Democrats of exploiting the chaos and trauma of last month's Capitol riot for their party's gain.

In a brief filed just hours ahead of the start of the trial, Trump's lawyers argued that the former president was speaking only in a "figurative sense" to his supporters.

They will also likely argue that Trump was simply exercising his First Amendment freedom of speech rights when he disputed the election results. Also, since he explicitly encouraged his supporters to have a peaceful protest, Trump cannot be held responsible for the actions of a handful of rioters, his team has said.

What will the prosecution argue?

The nine Democrat House impeachment managers filed their own brief Monday asserting that Trump had "betrayed the American people" and that there is no valid excuse or defense for what occurred on January 6.

"His incitement of insurrection against the United States government, which disrupted a peaceful transfer of power, is the most grievous constitutional crime ever committed by a president," they said.

To make their case, prosecutors are expected to rely on videos from the siege, first-person accounts from various lawmakers, along with Trump's public speeches and incendiary rhetoric refusing to concede the election.

Additionally, many of the senators are themselves witnesses.

What will be President Joe Biden's role?

There is no formal role for President Joe Biden during the trial. When asked about his plans during a briefing Monday, press secretary Jen Psaki answered that Biden will be busy with the business of the presidency and won't spend "too much time watching" the hearings.

What is the likelihood of conviction?

Trump is the first US president to be impeached twice. He is also the only one ever to face trial after leaving office.

Though Democrats argue it is necessary to hold Trump accountable for his actions, for Republicans, the trial will test their loyalty to the former president. It will also serve to showcase his enduring grip on the Republican party itself.  

Initially repulsed by the graphic images of the siege, Republican senators, including Senate minority leader Mitch McConnell, denounced the violence and pointed fingers of blame at Trump.

In the weeks since, however, others have softened their positions — with some Republicans saying it's not likely that they will vote to convict Trump.

What can happen to Trump?

Even if Trump is acquitted, the Senate could consider other motions such as censure, which requires only a simple majority.

However, even if Trump is convicted, it is not clear that is enough to prevent him from ever holding office in the future. 

According to the New York Times and other US media outlets, barring Trump from ever running or holding office again may require yet another vote in the Senate.

Trump, who is 74 years old, has not dismissed another presidential run in 2024.

Regardless of the impeachment trial's outcome, Trump remains the target of multiple investigations in several state and federal courts, both connected to the events of January 6 and other legal questions.

It is likely that the impeachment trial will only be the first of several post-presidential court battles. 

mb/rs (Reuters, AP)