The impeachment trial of US President Donald Trump marched ahead today with the second of three days for the Democrats' opening arguments.

The House impeachment managers (aka the prosecutors) zeroed in on the first article of impeachment, which charges the President with abusing his power by withholding military aid from Ukraine in exchange for an investigation into his political rivals.

Senators, who'll soon vote on whether Mr Trump will remain in office, listened (and occasionally snoozed) in mandated silence.

Here's a bit of what they saw:

1. Democrats stayed consistent in their strategy

The impeachment managers began their opening arguments yesterday by presenting a comprehensive, uber-detailed chronology of the events that led to the whistleblower's complaint.

US President Donald Trump's personal attorney Jay Sekulow speaks to reporters near the Senate subway in the US Capitol during a dinner recess. ( Reuters: Sarah Silbiger )

Today, they took those facts and applied them to the laws.

They started by walking through the constitutional standards at hand, delivering the Senate a history lesson on why impeachment doesn't require a criminal violation.

Representative Jerry Nadler indulged in a little legal trolling by using clips of Republican Senator Lindsey Graham — a staunch impeachment opponent — defining "high crimes and misdemeanours" during Bill Clinton's 1999 trial, but for the most part, the arguments were not unexpected.

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With the legal parameters out of the way, the House managers presented evidence that the President abused his power by pressuring Ukraine to investigate his political rival.

At the heart of that argument was a lengthy discussion of the President's motivation. The Democrats claimed that Mr Trump was never really interested in investigating corruption but only wanted to undermine 2020 presidential frontrunner Joe Biden.

That approach necessitated a lengthy defence of the candidate — and plenty of flack from Republicans for it (more on that below).

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It also meant debunking, step-by-step, some of the falsehoods Mr Trump has repeated to accuse Ukraine — not Russia — of hacking the 2016 Presidential election.

"If this sounds far-fetched and crazy, it is," said Representative Sylvia Garcia at the end of it.

"There are literally no concrete facts to support these conspiracy theories."

Like yesterday, the Democrats made slick use of graphics, news coverage and clips of witness testimony throughout their presentation.

And, like yesterday, the Democrats didn't make any points that haven't already been made. They just repackaged them in a linear, fluid format.

2. Witnesses are still divisive

Throughout their arguments, the impeachment managers drew attention to missing documents or witnesses they'd like to question.

It might seem counterintuitive given they keep saying there's "overwhelming evidence" that Mr Trump did wrong. But the new evidence has emerged as a major talking point, with Republicans repeatedly dismissing the trial because it doesn't show them something new.

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Democratic Senate minority leader Chuck Schumer told reporters he still had hope that Republicans would change their minds and allow the Senate to call key witnesses like former national security adviser John Bolton.

Senators voted along party lines on Monday (local time) to table an amendment that would've made that a reality, but a handful of moderate Republicans have said they'd consider voting in favour of witnesses if the Senate brings it up again following questioning.

Mr Schumer denied rumours that a "witness trade" was in the works, but said the Senate has "lots of conversations going".

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3. Republicans gave us a sneak peek of their defence

Though Mr Trump's defence team wasn't allowed to speak in the chamber, they didn't hold back in front of reporters.

Mr Trump's personal lawyer Jay Sekulow said he hadn't heard anything that surprised him.

"We're hearing the same things over and over," he said.

"I will assure you this: We will be putting on a vigorous defence of the facts and rebutting what they've said. Our job here is to defend the President, the office of the presidency and the constitution."

US Senator Mike Rounds plays with a fidget spinner handed out to Republican senators at lunch to keep them occupied. ( Reuters: Susan Cornwell )

Mr Sekulow also suggested the defence would keep things brief, saying he wouldn't "try to run the clock out".

Republican Senators appeared irked by the Democrats' defence of Mr Biden and called for the defence to focus on his son, Hunter.

Senator Ted Cruz said the Democrats essentially "threw Joe Biden under the bus".

"It means when President Trump's lawyers stand up and present their defence, that they are going to have the opportunity to present the very significant evidence that's supported and still supports a serious investigation into corruption at Burisma and ultimately whether Joe Biden participated in that corruption," Mr Cruz said.

"That consequence now, as a result of this decision, Hunter Biden is not only relevant, he is now critical."

Mr Sekulow confirmed the defence team was considering a direct response to the Democrats' Biden claims.

4. Senators are still zoning out

Representative Adam Schiff's introduction to the day said it all. His first words were an apology to Senators for such long days and dense material.

"There is some method in our madness," he added.

"We showed you the facts. Now we will show you how those facts are interwoven."

But in the end, reporters caught Senators doing everything but watching. They were sleeping, snacking, doodling, passing notes, doing crossword puzzles, reading a book — even leaving their seats to do interviews.

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Sorry, Senators. This thing is far from over.

The Democrats plan to close out their opening arguments on Friday (local time) by applying the evidence to article two, which covers obstruction of congress.

They'll also explain why they think Mr Trump is an ongoing threat to democracy.

So maybe the Senators won't pay attention, but history sure will.