The House January 6 select committee is expected to make the case at its seventh hearing Tuesday that Donald Trump gave the signal to the extremist groups that stormed the Capitol to target and obstruct the congressional certification of Joe Biden’s electoral college win.

The panel will zero in on a pivotal tweet sent by the former president in the early hours of the morning on 19 December 2020, according to sources close to the inquiry who spoke on the condition of anonymity to discuss the forthcoming hearing.

“Big protest in D.C. on January 6th,” Trump said in the tweet. “Be there, will be wild!”

The select committee will say at the hearing – led by congressmen Jamie Raskin and Stephanie Murphy – that Trump’s tweet was the catalyst that triggered the Proud Boys and Oath Keepers groups, as well as Stop the Steal activists, to target the certification.

And Trump sent the tweet knowing that for those groups, it amounted to a confirmation that they should put into motion their plans for January 6, the select committee will say, and encouraged thousands of other supporters to also march on the Capitol for a protest.

The tweet was the pivotal moment in the timeline leading up to the Capitol attack, the select committee will say, since it was from that point that the Proud Boys and Oath Keepers seriously started preparations, and Stop the Steal started applying for permits.

The select committee also currently plans to play video clips from former White House counsel Pat Cipollone’s recent testimony to House investigators at Tuesday’s hearing.

Raskin is expected to first touch on the immediate events before the tweet: a contentious White House meeting on 18 December 2020 where Trump weighed seizing voting machines and appointing conspiracy theorist Sidney Powell as special counsel to investigate election fraud.

The meeting involved Trump and four informal advisers, the Guardian has reported, including Trump’s ex-national security adviser, Michael Flynn, ex-Trump campaign lawyer Sidney Powell, ex-Overstock CEO Patrick Byrne and ex-Trump aide Emily Newman.

Once in the Oval Office, they implored Trump to invoke executive order 13848, which granted him emergency powers in the event of foreign interference in the election – though that had not happened – to seize voting machines and install Powell as special counsel.

The former president ultimately demurred on both of the proposals. But after the Flynn-Powell-Byrne-Newman plan for him to overturn the election fell apart, the select committee will say, he turned his attention to January 6 as his final chance and sent his tweet.

The response to Trump’s tweet was direct and immediate, the panel will show, noting that Stop the Steal announced plans for a protest in Washington set to coincide with Biden’s certification just hours after the former president sent his missive.

The Proud Boys – whose top members has since been indicted for seditious conspiracy over the Capitol attack – also started to crystalize what their plans were for January 6 the following day, according to federal prosecutors prosecuting the case.

On 20 December 2020, prosecutors have said, the former Proud Boys national chairman Enrique Tarrio created an encrypted group chat called “MOSD Leaders Group” – described by Tarrio as a “national rally planning” committee that included his top lieutenants.

The day after Tarrio started the MOSD Leaders Group – the Monday after Trump’s tweet that came on a Saturday – the leaders of Stop the Steal applied for a permit to stage a protest on “Lot 8” near the Capitol, and around that time, sent live the WildProtest.com website.

Through the rest of December and spurred on by Trump’s tweet, the select committee will say citing the Proud Boys indictment, the Proud Boys leaders used the MOSD chats to plan a “DC trip” and tell their members to dress incognito for their operation on January 6.

Top members of the Oath Keepers militia group led by Stewart Rhodes, who have also been indicted for seditious conspiracy, made similar plans as they prepared to obstruct the congressional certification of Biden’s election win, the panel intends to show.

The select committee will then focus on how the Oath Keepers stockpiled weapons and created an armed quick reaction force ready to deploy to the Capitol, and how the group ended up as the security detail for far-right activist Roger Stone and other Trump allies.

One of the witnesses providing public testimony at the hearing is expected to be Jason van Tatenhove, a former spokesperson for the Oath Keepers who left the group around 2017 but is slated to discuss their motivations and how they operated.

The 1st Amendment Praetorian, Flynn’s paramilitary group, is also expected to get a brief mention at the hearing, as will the various “war rooms” at the Willard hotel, where both Stone and Flynn, as well as Trump’s attorney, Rudy Giuliani, were spotted ahead of January 6.

The select committee, through Raskin’s portion of the hearing, will run through the effects of Trump’s tweet on preparations for January 6 right up until the morning of the Capitol attack and Trump’s speech at the Save America rally on the Ellipse.

Congresswoman Murphy is then expected examine the Ellipse rally itself, and Trump’s incendiary rhetoric where he told his supporters that he would march with them to the Capitol, giving the pro-Trump crowd the ultimate incentive to storm Biden’s certification.