WASHINGTON – Claims by former President Donald Trump's lawyers that his conduct around the Jan. 6 Capitol riot is shielded by the First Amendment are "legally frivolous" and should do nothing to stop the Senate from convicting him in his impeachment trial, 144 leading First Amendment lawyers and constitutional scholars from across the political spectrum wrote in a letter circulated Friday.

Taking aim at one of the key planks of Trump's defense, the lawyers argued that the constitutional protections do not apply to an impeachment proceeding, were never meant to protect conduct like Trump's anyway and would most likely fail to shield him even in a criminal court.

"Although we differ from one another in our politics, disagree on many questions of constitutional law, and take different approaches to understanding the Constitution's text, history, and context, we all agree that any First Amendment defense raised by President Trump's attorneys would be legally frivolous," the group wrote. "In other words, we all agree that the First Amendment does not prevent the Senate from convicting President Trump and disqualifying him from holding future office."

Among the lawyers, scholars and litigants who signed the letter were Floyd Abrams, who has fought marquee First Amendment cases in court; Steven Calabresi, a founder of the conservative Federalist Society; Charles Fried, a solicitor general under President Ronald Reagan, and preeminent constitutional law scholars like Laurence Tribe, Richard Primus and Martha Minow.

The public retort came after Trump's lawyers, Bruce Castor and David Schoen, indicated this week that they planned to use the First Amendment as part of their defense when the trial opens Tuesday. They argued in a written filing that the House's "incitement of insurrection" charge "violates the 45th president's right to free speech and thought" and that the First Amendment specifically protects Trump from being punished for his baseless claims about widespread election fraud.

The House impeachment managers have argued that Trump's false statements claiming to have been the true winner of the election, and his exhortations to his followers to go to the Capitol and "fight like hell" to reverse the outcome, helped incite the attack.

In their letter, the constitutional law scholars laid out three counterarguments to the president's free-speech defense that the Democrats prosecuting the case were expected to embrace at trial.

First, they asserted that the First Amendment, which is meant to protect citizens from government limits on their free speech and other rights, has no real place in an impeachment trial. Senators are not determining whether Trump's conduct was criminal but whether it sufficiently violated his oath of office to warrant conviction and potential disqualification from holding future office.

"As a result, asking whether President Trump was engaged in lawful First Amendment activity misses the point entirely," they wrote. "Regardless of whether President Trump's conduct on and around January 6 was lawful, he may be constitutionally convicted in an impeachment trial if the Senate determines that his behavior was a sufficiently egregious violation of his oath of office to constitute a 'high crime or misdemeanor' under the Constitution."

What is more, they argued, even if the First Amendment did apply to an impeachment trial, it would do nothing to bar conviction, which has to do with whether Trump violated his oath, not whether he should be allowed to say what he said.

"No reasonable scholar or jurist could conclude that President Trump had a First Amendment right to incite a violent attack on the seat of the legislative branch, or then to sit back and watch on television as Congress was terrorized and the Capitol sacked," they wrote.

Finally, they contended that there was an "extraordinarily strong argument" that the defense would fail even in a criminal trial because the evidence against Trump is most likely strong enough to meet the Supreme Court's high bar for punishing someone for inciting others to engage in unlawful conduct.

Many of the signatories to Friday's letter had signed on to a previous one pushing back on another key argument in Trump's defense: the assertion that the Senate does not have jurisdiction to try a former president because the Constitution does not explicitly grant it that power.

The letter emerged as Trump's legal team, which was hastily pulled together in recent days after he dismissed his original impeachment lawyers, worked feverishly to get up to speed on the case and prepare for the trial.