Even with acquittal seemingly assured, US Democrats prosecuting President Donald Trump in his impeachment trial have made a forceful appeal for conviction, calling him a man with no moral compass who must be removed to protect American democracy.

Representative Adam Schiff wrapped up closing arguments on Monday for the seven House of Representatives impeachment managers after Mr Trump's lawyers called the case against the Republican president politically motivated, reckless and baseless.

Senate Television/AAP

"We have proven Donald Trump guilty. Now do impartial justice and convict him," Mr Schiff told the 100-member Senate.

"He has betrayed our national security and he will do so again. He has compromised our elections and he will do so again. You will not change him. You cannot constrain him.

"If you find the courage to stand up to him, to speak the awful truth to his rank falsehood, your place will be among the Davids who took on Goliath - if only you will say, 'Enough.'"

The impeachment drama neared its conclusion a day before Mr Trump is due to give his annual State of the Union speech to Congress.

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READ MORE US Senate votes against calling witnesses in Donald Trump's impeachment trial

On Wednesday, the Republican-controlled Senate is set to vote on whether to remove Mr Trump from office.

None of the 53 Senate Republicans has called for conviction.

The Democratic-led House impeached Trump on December 18 on charges of abuse of power for asking Ukraine to investigate political rival Joe Biden and obstruction of Congress for blocking testimony and documents sought in the investigation.

Mr Trump has called the impeachment effort an attempted coup by Democrats.

Mr Schiff said America's founders intended impeachment - the power given to Congress under the US Constitution to remove a president for committing "high crimes and misdemeanours" - to be used rarely.

But he said it must be used to remove a president who "would sell out his country for a political favour," undermine the integrity of elections and invite foreign interference in American affairs.

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Mr Schiff said Mr Trump, if left in office, would continue to invite foreign interference in November's election, in which he is seeking re-election. Mr Biden is a leading contender for the Democratic nomination.

"What are the odds if left in office that he will continue trying to cheat? I will tell you: 100 per cent," Mr Schiff said.

"A president free of accountability is a danger to the beating heart of our democracy."

The Senate voted on Friday not to hear from any witnesses, including Mr Trump's former national security adviser John Bolton, who in an unpublished book depicts Mr Trump as playing a central role in pressuring Ukraine.

Only two Republicans, moderates Mitt Romney and Susan Collins, voted to hear witnesses.