Liz Cheney, the third most senior Republican in the House of Representatives, has raised the possibility of Donald Trump being criminally investigated for provoking violence during the 6 January US Capitol insurrection, pointing to a tweet attacking his own vice-president, Mike Pence, that was posted after the assault had begun. In extraordinary remarks on Fox News Sunday, Cheney made specific reference to the “massive criminal investigation” on the Capitol insurrection that is now sweeping the country. She said that the probe would cover “every aspect” of the events of 6 January and look at “everyone who was involved”. But she reserved her most pointed words for Trump. “People will want to know what the president was doing,” she said. “They will want to know whether the tweet that he sent out calling Vice-President Mike Pence a coward while the attack was underway was a premeditated attempt to provoke violence.” Cheney’s evoking of possible criminal action against the former president comes just two days before the start of his impeachment trial in the US senate for “incitement of insurrection”. Though she will not be participating as a juror at the trial – that role is performed by senators – her comments signaled the turmoil that the impending proceedings are causing in her party. Last week she survived an attempt by fellow House Republicans to remove her from her leadership position in protest at her support of Trump’s impeachment. On Saturday, the Republican party in her home state of Wyoming voted to censure her, calling for her immediate resignation. Cheney said Sunday she would not step down. “The oath I took to the constitution compelled me to vote for impeachment – it does not bend to partisanship or political pressure, and I will stand by that.” But the swirl of criticism around her, coupled with her sharp reference to possible criminal consequences for Trump, point to how the former president continues to roil the Republican party, to the extent of threatening to tear it apart. On Tuesday, he will make US history by becoming the first sitting or former president to be subjected to an impeachment trial for a second time. Ahead of the historic proceedings, prominent Democrats took to the Sunday political shows and spoke with passion about why Trump deserved to be convicted for his role in allegedly inciting the 6 January assault. Ayanna Pressley, a congresswoman from Massachusetts, called on senators to “honor their oath and hold Trump accountable and bar him from ever holding office again”. Speaking on CNN’s State of the Union, she recalled the “harrowing and traumatic” assault on the Capitol and placed it in personal and historical context. “As a black woman, to be barricaded in my office, on the ground, in the dark – that terror is familiar in a deep and ancestral way for me.” She said she was haunted by the image of black staff in the Capitol building cleaning up the mess caused by the white supremacist insurrection. “That is a metaphor for America. We have been cleaning up for white supremacist mobs for generations – and it must end,” she said. By contrast, there was little sign among Republican senators of any substantial appetite to convict. Should all 50 Democratic senators vote to do so, they would still need to be joined by 17 Republican senators to reach the two-thirds majority required by the constitution. Rand Paul, the Republican senator from Kentucky, said Tuesday’s trial was an attempt to criminalise political speech. Speaking on Fox News Sunday, he said: “Are we going to impeach and potentially criminally prosecute people for political speech when they say ‘Get up and fight for your country, let your voices be heard’?” The Republican senator from Louisiana, Bill Cassidy, told NBC News’s Meet the Press that the trial had been rushed. “There was no process. If it happened in the Soviet Union you would call it a show trial.” Pat Toomey, the Republican senator from Pennsylvania who has been critical of Trump, told CNN that he thought it “very unlikely” that the former president would be convicted. Without conviction, senators would not be able to move to a further vote to bar Trump from ever holding public office. The case for impeachment will be presented to senators by House managers. In their brief, they allege that Trump “summoned a mob to Washington, exhorted them into a frenzy, and aimed them like a loaded cannon down Pennsylvania Avenue”. In a 14-page rebuttal, Trump’s lawyers argue that he did not engage in insurrection and that impeaching him as a former president is unconstitutional. The evidence stage of the Senate trial is likely to focus on Trump’s remarks leading up to the violence on 6 January, which left five people dead. At a rally earlier in the day, Trump used visceral language, saying “we will not take it any more” and “you’ll never take back our country with weakness”. It is not known whether impeachment managers plan to single out Trump’s tweet attacking Pence. In the tweet, which has now been removed from Twitter as part of Trump’s suspension from the platform, he criticised the then vice-president for failing to block counting of the electoral college results of the presidential election that Trump lost. “Mike Pence didn’t have the courage to do what should have been done,” Trump posted. The tweet was posted about 10 minutes after it was reported that Pence had been ushered off the floor of the Senate following the violent breach of the Capitol by Trump supporters and white supremacists. During the attack, members of the mob could be heard chanting “hang Mike Pence”.