Trump's lawyer, Jesse Binnall, said during a court hearing that Trump was "immune," or shielded, from three lawsuits by Democratic members of Congress and two police officers.
"Executive immunity must be broad," Binnall told the court on Monday.
The lawsuits, filed by plaintiffs including Democratic US representatives Eric Swalwell and Jerry Nadler, argue that Trump is liable for injuries to police and lawmakers.
Looming large in the case is a Supreme Court case from 1982 holding that presidents are immune from lawsuits over their official acts.
During a court hearing, which was ongoing, US District Judge Amit Mehta repeatedly pressed lawyers for both sides about the limits of this presidential immunity.
Plaintiffs lawyer Joseph Sellers countered that Trump's speech was a campaign event, not an official act and said it was "inconceivable" that the Supreme Court intended to shield presidents from lawsuits over this sort of conduct.
"There is no legitimate role for fomenting an insurrection aimed at Congress," Sellers said.
The Democratic lawmakers have invoked an 1871 law passed to fight the white supremacist Ku Klux Klan that prohibits political intimidation.
The lawsuits charge that the worst attack on the US Capitol since the War of 1812 was a direct consequence of Trump's actions, including the speech to thousands of supporters who then stormed the building to try to overturn President Joe Biden's election.
Mehta was unlikely to issue a ruling on Monday, but the hearing may shed light on whether Trump and allies can be held liable in a civil court for the deadly Capitol siege.
Trump was impeached by the House of Representatives and acquitted by the Senate on a charge of inciting the riot, which is also under investigation by a House select committee.
Swalwell's lawsuit includes similar claims against Trump allies who also spoke at the January 6 rally, including campaign lawyer Rudy Giuliani, Trump's eldest son Donald Trump Jr, and Republican congressman Mo Brooks.
Brooks has sought to dismiss Swalwell's claims, arguing his remarks at the January 6 rally were within the scope of his duties as a House member. A law called the Westfall Act protects federal employees from being sued for actions taken as part of their jobs.
Trump and his co-defendants have argued that their remarks preceding the January 6 attack were political speech protected by the First Amendment of the US Constitution.
The two Capitol Police officers who sued Trump are James Blassingame and Sidney Hemby.
