Andrew Cohen, a former Washington correspondent with The Globe, is author of Two Days in June: John F. Kennedy and the 48 Hours That Made History.

Parse his words. Hear his agony. Hail his integrity or doubt his credibility. Cheer his courage or jeer his silence.

Marvel at his quaint exclamations from "Holy cow!" to "Lordy." Follow shades of expression like the changing light of winter: stony, stern, dark, immobile, quizzical, his face unbroken by the trace of a smile for the first 56 minutes. This is a serious man with a serious complaint.

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If you are a Democrat, identify and salute the truths he speaks to power and underscore when and how; if you are a Republican, identify and lament the truths unspoken and ask why. Look for "the smoking gun" that will break this investigation wide open, threatening to unseat this president – or the ambiguity or uncertainty that will exonerate him.

Read more: Comey speaks: Highlights from his testimony on Trump and Russia

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Lawrence Martin: Trump gets a pass on the Russia probe – for now

All that is the veneer of what happened in the Senate of the United States on Thursday morning. Of course, what James Comey has to say about his short, unhappy association with Donald Trump is what everyone is discussing today. This happens when politics produces a rare spectacle as his, compelling the three television networks to break into regular programming, joining the all-news networks, online streaming, running commentary on newspaper websites and other boasts of social media, throbbing with the same giddy obsession.

But understand what took place when Mr. Comey, former director of the Federal Bureau of Investigation, entered Room 216 of the Philip A. Hart Senate Office Building, raised his right hand, swore an oath and began to recall the falsehoods and distortions, as he saw them, of the President of the United States.

Understand what it means when the head of the country's leading law enforcement agency calls its commander-in-chief "a liar." Or, when the President calls Mr. Comey "a nut job," finds him disloyal and fires him.

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In Comey vs. Trump, we have a new American Melodrama. The accuser is the nation's oldest boy scout, freshly scrubbed and buttoned-down, in the dock in muted burgundy tie, white shirt and blue suit. He is earnest and saturnine. The defendant is the nation's braggart and bully, his administration now entangled in three major investigations, any one of which could undo him.

Thursday's hearing was a moment in the life of a polarized country at war with itself for the last generation. Some call it a cultural war. It manifests itself in the political theatre that thrives in the hothouse of the United States. As with those once-in-a-lifetime floods, though, it seems to occur more often.

It happened around Joe McCarthy and the army in the 1950s, Richard Nixon and Watergate in the 1970s, Oliver North and Iran-Contra in the 1980s, Anita Hill and Clarence Thomas in the 1990s. It is when American puts its democracy on trial. It is messy but necessary. Some countries have royal commissions or parliamentary panels; the United States has congressional hearings. To Americans, it's the greatest show on earth.

Mr. Comey's testimony – and the looming spectre of "high crimes and misdemeanours" – recalls the impeachment of Bill Clinton. When news broke of Monica Lewinsky's liaison with Mr. Clinton in January, 1998, my colleagues and I writing the story avoided discussing "impeachment." Whatever its shock value in a headline (long before "jaw-dropping clickbait"), I resisted the notion when my editor raised it early on. I did not believe that it would happen until it did, one Saturday morning in December, as I sat watching in the gallery of the House of Representatives.

Impeachment, a political indictment, had not happened since 1868 when the House impeached Andrew Johnson. He was narrowly absolved by the Senate, after a sensational trial.

In 1998, though, impeachment seemed implausible. But it was not entirely remote, either. In 1974, a House committee passed articles of impeachment, which the House was ready to adopt before Mr. Nixon resigned.

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Today, talk of impeachment is strikingly common; it is discussed cavalierly by the chorus of commentators – scholars, journalists, prosecutors – who annotate these hearings. In fact, it has been used in some circles since the day President Trump arrived.

So, when Mr. Comey spoke of how the president "lied" and "defamed" him, or how he feared being in the same room alone, (the way some women are reluctant to be alone with a male doctor), he was making the opening argument in the trial of Donald Trump. When Republicans attacked Mr. Comey and Democrats defended him, they were each playing their role, too. As were the media and millions of Americans watching. This exercise is a predictable, peculiarly American institution.

Now the show has begun, again. It will play for some time – and assuredly return again.