Democrats and Republicans in the US Senate remained at loggerheads on Friday over how to proceed with the impeachment trial of President Donald Trump.

As lawmakers returned from a two-week holiday recess, it was still not clear when the trial would begin.

Senate Majority Leader Mitch McConnell, a Republican, accused House Democrats of getting “cold feet” by choosing not to immediately send the articles of impeachment to the Senate after voting to impeach Trump in December.

“We can’t hold a trial without the articles,” McConnell said.

“We should address mid-trial questions such as witnesses after briefs, opening arguments, senator questions and other relevant motions,” he added, arguing that this would follow the precedent set in former President Bill Clinton’s impeachment trial twenty years ago.

But Senate Democratic Leader Chuck Schumer countered that McConnell was setting a “trap” by waiting to consider witnesses until after opening presentations.

“There has never, never in the history of our country been an impeachment trial of a president in which the Senate was denied the ability to hear from witnesses,” Schumer said.

He has asked the acting White House chief of staff Mick Mulvaney and former national security adviser John Bolton, as well as two other White House aides, to testify.

Trump maintains he did nothing wrong.

He is accused of abusing his office by soliciting Ukraine to dig up dirt on former vice president Joe Biden, a leading candidate among Democrats bidding to run against Trump this year.

The president is expected to be acquitted by the Republican-controlled Senate. (NAN)