Nancy Pelosi, the House Speaker, is preparing the committee that will begin its investigation into the Capitol attack on Tuesday to launch an aggressive investigation into Donald Trump, hoping to capitalize on a Republican refusal to participate that could leave the former president vulnerable.

Pelosi’s decision last week to bar Jim Banks and Jim Jordan, both vocal Trump supporters, from serving on the House select committee prompted House Minority Leader Kevin McCarthy to boycott the inquiry, withdrawing his three other Republican nominees. However, Pelosi received strong Democratic support and told lieutenants that she may have gained the upper hand ahead of the select committee’s first hearing.

According to a source familiar with the situation, the speaker has recently suggested to top Democrats that McCarthy’s decision to boycott the panel leaves Trump without any defenders in the high-profile investigation into the 6 January insurgency.

Pelosi appointed some of the former president’s most vexing opponents to the select committee, including both lead impeachment managers from Trump’s two impeachments, as well as Republican dissident Liz Cheney, who was ousted from party leadership in May for opposing Trump.

On Sunday, she added a second Republican, Adam Kinzinger of Illinois, who has also spoken out against the Capitol attack.

The lack of Republican nominees on the committee means that when the investigation shifts from examining security failures to Trump’s role on January 6, the inquiry will be conducted solely by his political opponents, emboldening Pelosi to seek an aggressive investigation, according to the source.

Democrats have been urging Pelosi to take a tough stance against Republicans for weeks, after the party in the Senate blocked a 9/11-style bipartisan commission into the Capitol attack.

Democrats close to Pelosi say she is still enraged by Republicans’ attempts to downplay the insurgency’s brutal violence, which influenced her decision not to give Banks and Jordan a platform from which to twist or minimize the select committee’s findings.

The speaker’s relationship with Republicans, however, reached a new low after McCarthy yelled down the phone at her when she informed him of her decision to veto Banks and Jordan, according to a source.

Republicans have used Pelosi’s intervention against Banks and Jordan, as well as her close involvement with the panel, to portray the investigation as a partisan exercise aimed at gaining political advantage ahead of the 2022 midterm elections.

McCarthy reacted angrily a day after being denied his two top committee picks, vowing to conduct a Republican-only investigation into how Pelosi could have done more to protect the Capitol.

Democrats, on the other hand, said Pelosi was more than justified in defying congressional norms by refusing to appoint Banks and Jordan, both of whom amplify Trump’s lies about a stolen election and objected to certifying Joe Biden’s election victory.

They also claimed that Pelosi came to the conclusion that Banks could not be trusted to serve as the panel’s top Republican after he stated his desire to investigate the role of the Biden administration in the insurgency.

Democrats expressed grave concerns about Jordan, the top Republican on the House judiciary committee, after he disparaged the select committee and accused Pelosi of being responsible for the Capitol’s diminished security presence.

The speaker is not in charge of Capitol security, which is handled by the US Capitol police board and the House and Senate sergeants-at-arms. Republican leaders hired both sergeants-at-arms at the time of the attack.

A bipartisan Senate report issued last month detailed numerous security flaws on the part of the US Capitol police and sergeants-at-arms. It did not blame Pelosi or her then opposite number in the Senate, Mitch McConnell.