Donald Trump's trial on charges of covering up hush money payments to a porn star approached its final stages on Monday, with closing arguments expected early next week.

Due to an upcoming holiday weekend as well as legal squabbles over jury instructions among other yet undisclosed "issues," Judge Juan Merchan told the court "it's become apparent that we are not going to be able to sum up tomorrow" as he had hoped.

It's still unclear if the defence will present a case – they are not required to – or whether Trump himself will testify.

Most experts say it is highly unlikely he will take the stand in his watershed criminal trial, the first ever of a former US president, as it would expose him to unnecessary legal jeopardy and forensic cross-examination by prosecutors.

But Trump's lawyer Todd Blanche has raised the prospect his client could step up as a witness, telling the judge last week "that's another decision we need to consider."

Before the prosecution can rest, defence lawyers will first conclude grilling the state's star witness, Michael Cohen.

Cohen, Trump's former personal lawyer and fixer turned tormentor, recounted last week how he kept Trump informed about US$130,000 paid to porn star Stormy Daniels to buy her silence about an alleged affair ahead of the 2016 presidential election.

Over several days of questioning that continued on Monday, Trump's lawyers have set out to paint Cohen as a convicted criminal and habitual liar, recalling his time in prison for tax fraud and lying to Congress.

Blanche has also probed Cohen's loyalty both past and present, to Trump and the prosecution respectively, looking to show jurors that the former fixer is self-serving and willing to go to great lengths to accomplish his aims.

Cohen has said repeatedly he takes "responsibility" for his actions and has faced the consequences. Prior to the trial, including in his books, he had done little to hide his contempt for his former boss.

Blanche has striven to ruffle Cohen, who has a reputation for a temper that could hurt him on the stand – but the witness has stayed largely composed and on topic.

Cohen's story has generally lined up with Daniels and David Pecker, the tabloid boss who said he worked with Trump and Cohen to suppress negative coverage during the Republican's 2016 White House run. (AFP)