Former US president Donald Trump announced Sunday he had picked two lawyers to head his defense team days before his historic second impeachment trial, as Republicans braced for a battle over the future of their party.

Trump's Senate trial is due to start on February 9, but he had reportedly parted ways with several members of his initial legal team just a day ago.

His lead lawyers, David Schoen and Bruce L. Castor, Jr, are "highly respected trial lawyers" with backgrounds in criminal law and defense, according to a statement from Trump.

Schoen has represented Trump ally Roger Stone, and said he was in discussions to join the legal team for Jeffrey Epstein in 2019 days before the disgraced US financier killed himself while in jail on allegations of trafficking underage girls for sex.

Castor previously served as the district attorney for Montgomery County, Pennsylvania, where he declined to push forward with a case when US comedian Bill Cosby was accused of sexual assault by Andrea Constand.

The case moved forward under Castor's successor and Cosby was convicted in 2018. Schoen had already been working with the defense team, and both he and Castor "agree that this impeachment is unconstitutional," Trump's statement said.

The trial of the former president for alleged "incitement of insurrection" over the storming of the Capitol by his supporters has exposed a rift between Trump loyalists who dominate the Republican Party, and its moderate wing.

"The Senate trial... is going to call all Republicans to take a position more clearly," Arkansas Governor Asa Hutchinson told ABC's "This Week."

He added: "We've got to have a regard for those people that supported Donald Trump... But at the same time, we don't want to gloss over the terrible actions that happened at the Capitol."

Trump looks increasingly likely to avoid conviction due to party support in the Senate -- where all but five Republicans already backed an attempt to throw out the case on constitutional grounds.

But the trial is still sure to see battle lines drawn over who controls the party following Trump's first-term defeat.

On January 6, Trump gave a fiery speech outside the White House exhorting his supporters to march on the US Capitol to overturn the election results.

Still Trump's party?

The protesters then violently stormed the Capitol building in scenes that shocked the world.

"The president's comments that day were partly responsible for what happened, for the horrible violence," Republican Senator Rob Portman told CNN's "State of the Union." "What he did was wrong and inexcusable.

"I am a juror. I'm going to keep an open mind as we go through this (trial). But I do think that this constitutionality issue has to be addressed. We would be convicting a private citizen, someone who's out of office. That sets up a precedent."

Adam Kinzinger, one of 10 Republicans in the House of Representatives to vote for impeachment earlier this month, said Sunday that Trump was "desperate to continue to look like he's leading the party."

"We need to quit being the party that even an iota defends an insurrection, a dead police officer and other dead Americans on the Capitol," Kinzinger told NBC's "Meet the Press."

Kinzinger has launched a new political action committee seeking to raise funds to challenge the Trump wing of the party.

While signaling opposition to Trump's trial, Republican senators are instead fueling efforts to censure him over his role in the Capitol assault.

But, while a conviction would lead to a simple-majority vote on whether to bar Trump from holding future public office, a censure resolution carries no such trigger.

Republican divisions have been further exposed in recent days by the newly-elected lawmaker Marjorie Taylor Greene, who has promoted the unhinged conspiracy theories pushed by the QAnon far-right movement, and has backed Trump's false claims of election fraud.

Party leaders are under pressure to take action against the lawmaker, whose past online posts have indicated support for executing Democrats and claimed school shootings were staged to undermine backing for gun rights.

But Taylor Greene has remained defiant, tweeting Saturday that she had had a "GREAT call" with Trump as she casts herself as a new champion of the party's Trumpist wing.