WASHINGTON — This matters.

The outcome may seem preordained in the unprecedented second impeachment trial of Donald Trump.

Democrats prosecuting the former president for inciting a deadly insurrection at the U.S. Capitol will struggle to persuade at least 17 Republicans to convict Trump and bar him from office. Forty-five of the 50 Republican senators backed a bid last month to dismiss the trial, essentially telegraphing how the final vote will play out.

But the trial set to begin Tuesday is ultimately a test of whether a president, holding an office that many of the nation’s founders feared could become too powerful in the wrong hands, is above the law. Senators will be forced to sit still, listen to evidence and wrestle with elemental questions about American democracy. There will be visual, visceral evidence, and the American people will also be sitting in their own form of judgment as they watch.

The verdict and the process itself will be scrutinized for generations.

“For historians, what that trial does is to provide additional evidence and documentation under oath,” said Carol Anderson, a professor of African American studies at Emory University. “It also gives us a sense of the strength, or the weakness, in American democracy as the senators are confronted with this evidence.”

That record is certain to be grisly, a reminder on a human level of the horror at the Capitol on Jan. 6.

Senators will review Trump’s call that morning to “fight like hell” before the mob of loyalists showed up to Capitol Hill to do just that. Senators will be reminded of the rioters’ chants calling for then-Vice President Mike Pence’s hanging. House prosecutors could resurface the image of a police officer crushed between doors, blood trickling from his mouth, as the violent crowd moved in. There might be additional evidence of how another officer, Brian Sicknick, died defending the building.

If that’s not enough, senators will be reminded of their own vulnerability as they fled the mob entering their chamber — one of the most rarefied spaces in Washington — in fear of their lives.

And then they’ll have to decide whether there should be consequences. But the potential of an acquittal doesn’t mean the trial should be abandoned before it begins, said Rep. Val Demings, who was an impeachment manager in Trump’s first trial.