Washington, DC - Managers for the US House of Representatives impeachment case against President Donald Trump plan to present the constitutional grounds for removing Trump from office on the second day of their opening arguments before the Senate.

"We will go through the law, the constitution and the facts ... as it pertains to the president's abuse of power," said Adam Schiff, the lead House manager prosecuting Trump's impeachment trial in the Senate.

"Abuse of power" lies at the heart of House Democrats allegations against President Trump, who they say violated his oath of office by leveraging US military aid and a potential White House visit to pressure Ukraine to announce investigations in a political rival.

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During the House impeachment inquiry, three leading US constitutional scholars told the Judiciary Committee that Trump's conduct amounted to an impeachable offence.

House managers are expected to argue on Thursday that Trump abused his powers as president by using the levers of the office to improperly pressure Ukraine to announce an investigation of Democratic politician Joe Biden and advance a debunked conspiracy theory about Russian interference in the 2016 elections.

This artist sketch depicts impeachment manager Schiff presenting an argument in the impeachment trial of President Donald Trump [Dana Verkouteren/AP Photo]

Democrats say Trump's offences, which includes elements of bribery, extortion and misuse of office, amounts to a crime against the United States and the American people.

The US Constitution, adopted in 1789, provides that a president can be removed from office by impeachment for "bribery, treason or other high crimes and misdemeanours". Under the Democrats' theory of the case, abuse of power is a high crime.

All 100 senators - 53 Republicans, 45 Democrats and 2 independents - are sitting as jurors in the trial of Trump which is expected to last several weeks.

Senators are required to be present for the proceedings and must leave mobile phones and other devices outside the chamber.

Supreme Court Chief Justice John Roberts presides.

'Shaken our democratic system'

On the first day of opening arguments, some senators took copious handwritten notes as Schiff and his House colleagues presented. Others sat listening attentively. As proceedings wore on, a number of Republicans, unable to remain in their seats, got up and left the room temporarily.

In making their case to the Senate, the House managers are expected to cite the words of the US's founders who wrote extensively about impeachment in an 18th-century collection of public letters called the "Federalist Papers'".

"The consequences alone of [Trump's] actions have shaken our democratic system," Schiff said in opening remarks on Tuesday.

"If we don't stand up to this peril today, we will write our own decline with our own hand," he told senators.

The shift to legal and constitutional theory follows eight hours of Senate proceedings on Wednesday in which House managers detailed the timeline of Trump's pressure campaign on Ukraine.

"It's the first time our Republican colleagues have heard the whole argument eloquently, completely and concise," said Senator Chuck Schumer, the top Democrat.

Not a 'conventional politician'

Even as House managers seek to prove Trump pressured Ukraine, a number of Senate Republicans say they do not believe what the president did amounts to an impeachable offence.

"If it doesn't go beyond the information that we've got, it would be like what most Republicans have said, 'I would not have done it, it's inappropriate,'" said Senator Mike Braun, a Republican.

"I give even a little more latitude in the sense that his style is not that of a conventional politician," Braun told Al Jazeera.

House Intelligence Committee Chairman Adam Schiff delivered opening arguments on Wednesday [Reuters]

The American public remains sharply divided over impeachment, according to recent opinion surveys.

A new poll by the Pew Research Center showed 51 percent of Americans say Trump should be removed from office, while 46 percent say Trump should stay. The poll was conducted by a self-administered web survey of 12,638 US adults between January 6 and 19.

About 11 million TV viewers watched the start of the impeachment trial on Tuesday when legislators sparred for hours over calling witnesses and documents, according to Nielsen ratings data.

In addition to abuse of power, Trump faces impeachment for obstruction of Congress.

'We have all the material'

As the impeachment inquiry began, Trump issued a blanket order to officials in his administration to refuse to cooperate with the House, in effect stonewalling the House investigators.

Trump's refusal to cooperate has become a major point of contention in the Senate trial.

The second article of impeachment was for obstruction of Congress: covering up witnesses and documents from the American people.



This morning the President not only confessed to it, he bragged about it:



"Honestly, we have all the material. They don't have the material." pic.twitter.com/DPAEFHIDjS — Rep. Val Demings (@RepValDemings) January 22, 2020

Much of the debate in the Senate has revolved around Democrats' demands that the White House and other agencies turn over documents and make key witnesses available.

Despite being thousands away, Trump, who has denied any wrongdoing, appears to be keeping a close eye on the proceedings, breaking his own record for the most Twitter activity in a day while in office.

At a news conference at the World Economic Forum in Davos on Tuesday, Trump appeared to acknowledge that his administration has withheld documents and testimony to the disadvantage of House managers now trying the case before the Senate.

"Honestly, we have all the material. They don't have the material," Trump told reporters.