Donald Trump's second — and hopefully final — impeachment trial begins this week. Barring some unexpected development, we already know how it will end: The former president will be acquitted on the single charge of inciting the Jan. 6 Capitol insurrection that left five people dead. There just aren't 67 votes in the 100-member Senate to sustain a conviction.

"It's not a question of how the trial ends, it's a question of when it ends," Sen. Lindsey Graham (R-S.C.) said Sunday on CBS. "Republicans are going to view this as an unconstitutional exercise, and the only question is, will they call witnesses, how long does the trial take? But the outcome is really not in doubt."

Indeed, there seems to be a "let's just get this thing over with" air to the proceedings, which are expected to last only about a week. Democrats are torn between spending time and energy to hold Trump accountable and moving forward with President Biden's agenda, while Republicans clearly just want to move on.

So why have an impeachment trial at all?

For one thing, it is vital to get this history right, and right away. The Senate trial will document the events of the Jan. 6 insurrection, as well as why it happened — not just because of the "Stop the Steal" rally that preceded the riot, but because Trump and his allies spent the two months following the November election lying that it had been stolen from him, part of a bald attempt to overturn those election results and stay in office illegitimately.

"We think that every American should be aware of what happened — that the reason he was impeached by the House and the reason he should be convicted and disqualified from holding future federal office is to make sure that such an attack on our democracy and Constitution never happens again," Rep. Jamie Raskin, a Maryland Democrat who is leading the prosecution, told The New York Times.

Already, "alternative" stories about what happened on Jan. 6 are flourishing. The Wyoming GOP, for example, has falsely declared that the insurrection was "instigated by Antifa and BLM radicals," while Sen. Ron Johnson (R-Wis.) on Sunday baselessly suggested the impeachment might be a way for House Speaker Nancy Pelosi (D-Calif.) to divert the country's attention from her own, nonexistent culpability. The trial should dispel any such notions for Americans who are still interested in facts.

Believe it or not, there are still plenty of those folks. A new ABC/Ipsos poll says 56 percent of respondents agree that Trump should be convicted and prohibited from holding office in the future, while 43 percent disagree. The supporters include 92 percent of Democrats, which is no surprise, and also 54 percent of independent voters.

Just 15 percent of GOP respondents support conviction, but Trump seems to have slimmed his party's support considerably: Thousands of former Republican voters changed their registration in January, choosing instead to identify as Democrats and independents in swing states like Pennsylvania and Arizona. That suggests voters are imposing accountability on Trump and his party however they can. Senators have the power to impose a more immediate punishment, by prohibiting Trump from running for office again, and thus depriving him of the political leverage that goes along with that possibility.

Again, that probably won't happen. But the trial is still necessary — even if it doesn't result in a guilty verdict — simply because failing to even try is wrong. To accept the inevitability of Trump's impunity is to surrender to cynicism, to give up on the notion of ever getting justice for the grievous wrongdoing of our leaders, to shrug at an act that took dead aim at the heart of democracy. That just encourages the next wannabe authoritarian with designs on stealing an election.

Importantly, Senate Republicans who will vote for acquittal are not defending Trump on the merits. They're offering up constitutional dodges, engaging in whataboutism, or indulging in fresh rounds of conspiracy-mongering. For the most part, they aren't saying that Donald Trump is innocent of inciting insurrection. This week's trial puts them on the record. Let them explain — to their constituents, to the nation, to the judgment of history — why they're willing to give Trump a pass for intentionally doing injury to the constitution they are sworn to defend and uphold. The impeachment trial may not end in a guilty verdict, but it will bring clarity.