Washington: US lawmakers were set to focus Thursday on the pressure campaign mounted by Donald Trump against his vice president to help the defeated Republican leader overturn his 2020 presidential election defeat.

Liz Cheney, vice chair of the House committee investigating the Capitol riot, said its third June hearing would address Trump's "relentless effort" on January 6 2021 and in the days beforehand to cajole Mike Pence into rejecting Joe Biden's victory.

"As a federal judge has indicated, this likely violated two federal criminal statutes. President Trump had no factual basis for what he was doing and he had been told it was illegal," Cheney said on Twitter.

"Despite this, President Trump plotted with a lawyer named John Eastman and others to overturn the outcome of the election on January 6."

An aide to the committee said the hearing would look at Eastman's role in developing a plot for Trump to pressure Pence into subverting the election, backed by a bogus legal theory that represented a "grave danger to American democracy."

Cheney's tweet featured a clip of testimony from Trump White House attorney Eric Herschmann who told Eastman the day after the insurrection: "Get a great effing criminal defense lawyer. You're going to need it."

The committee is in the middle of a run of televised hearings on the insurrection mounted by a pro-Trump mob to overturn the results of the 2020 election.

It has already revealed testimony from many of Trump's closest allies who said he was told repeatedly he'd lost a fair fight to Biden but declared victory and pushed his election fraud narrative anyway.

As dozens of legal challenges dismissed as inept and ethically suspect failed in courts across the land, a desperate Trump turned to Pence for illegal help.

Trump used rally speeches and Twitter to exert intense pressure on Pence to abuse his position as president of the Senate to reject the election results as they were being ratified on January 6.

"We're going to show that that pressure campaign directly contributed to the attack on the Capitol, and it puts the vice president's life in danger," a select committee aide said.

- 'Hang Mike Pence' -

During his "Stop the Steal" rally ahead of the joint session of the House and Senate to ratify the election, Trump mentioned Pence numerous times as he told his supporters to march on the Capitol and "fight like hell."

But Pence wrote to Congress that the Founding Fathers never intended the vice president to have "unilateral authority" to overturn election counts, adding that "no vice president in American history has ever asserted such authority."

The mob whipped up by Trump threatened to hang Pence for failing to cooperate as they stormed the Capitol, and even erected a gallows in front of the building.

Cheney said last week that when the subject of the "hang Mike Pence" chants came up at the White House, Trump responded: "Maybe our supporters have the right idea" and that Pence "deserves" it.

As the dust settled over the coming days, Pence accused the media of bad faith in its assiduous focus on the insurrection, but he has since taken a stronger line with Trump as he gears up for a widely-expected tilt at the presidency in 2024. "The presidency belongs to the American people and the American people alone," he told the conservative Federalist Society.

"And frankly, there is no idea more un-American than the notion that any one person could choose the American president."

The panel will hear from J Michael Luttig, a renowned conservative legal scholar and retired federal judge who advised Pence he had no authority to intervene in the certification of the election.

"The only responsibility and power of the vice president under the constitution is to faithfully count the electoral college votes as they have been cast," Luttig tweeted the day before the insurrection.