No US president has abused power the way Donald Trump did towards Ukraine, impeachment trial prosecutors have said.

In the second day of arguments at Mr Trump's trial in the Senate, Democrats focused on the first article of impeachment, abuse of power.

Mr Trump is accused of seeking a political investigation into 2020-presidential candidate Joe Biden from Ukraine for his own gain to sway the election in his favour.

The House of Representatives impeached him last month, arguing that he abused his office by pressuring Ukraine by withholding crucial military aid.

He is also facing another article of obstruction of Congress for refusing to turn over documents or allow officials to testify in the House probe.

"No president has ever used his office to compel a foreign nation to help him cheat in our elections," said Jerrold Nadler, the chairman of the House Judiciary Committee.

Mr Nadler added that the nation's founders would be shocked.

"The president's conduct is wrong. It is illegal. It is dangerous," he said.

Democrats also slammed Mr Tump's claims that he had good reasons for pressuring Ukraine to investigate his political foes.

Texas representative Sylvia Garcia said it was Mr Trump who engaged in a shocking abuse of power, not former Vice President Joe Biden or other Trump foes.

There is "no evidence, nothing, nada"' to suggest that Mr Biden did anything improper in dealings with Ukraine, said the former judge.

"There was no basis for the investigation the president was pursuing and pushing. None. He was doing it only for his own political benefit," she said.

The Democrats' challenge is clear as they try to convince not just the Republican majority Senate but an American public divided over the Republican president in an election year.

Ahead of the day's proceedings, Senator Roy Blunt of Missouri said the Democrats were putting forward "admirable presentations."

But he said: "They've basically got about one hour of presentation, and they gave it six times on Tuesday and eight times yesterday. There's just not much new here."

Adam Schiff, the Democratic chairman of the House Intelligence Committee, stood before restless senators forced to sit silently for another long day there would be "some repetition of information" from the overview heard on day one.

But he promised a stitching together of the facts to an inevitable conclusion.

Senators were accused of falling asleep, playing games during the trial, with crossword puzzles, fidget spinners and a paper airplane being spotted during proceedings.

Senator Richard Burr handed out fidget spinners - small toys designed to be spun between the fingers, relieving stress or boredom - to his colleagues before Thursday's trial proceedings began.

The top Senate Democrat, Chuck Schumer, acknowledged on Thursday that many senators "really don't want to be here."

But Mr Schumer said Mr Schiff has been outlining a compelling case about Mr Trump's pressure on Ukraine and the scheme to cover up the charges.

Many Republicans are hearing it for only the first time.

Once reluctant to take on impeachment during an election year, Democrats are now marching towards a decision by the Senate that the American public also will judge. They are one-third of the way through 24 hours of opening arguments.

Mr Trump blasted the proceedings in a Thursday morning tweet, declaring them the "Most unfair & corrupt hearing in Congressional history!"

Democrats are expected to wrap up their arguments Friday, with Mr Trump's legal team set to make its case for up to three days beginning Saturday.

J ay Sekulow, a lawyer for the president, deflected rumours that the defense may wrap up in a single day.

"We're going to use a sufficient amount of time to defend our case and point out the inconsistencies of their case. We're not going to run out the clock," he said.

"I am confident that whether it is (completed) Saturday or Monday or Tuesday that the case will be made defending the president. I have no doubt."