The arguments by opposing lawyers in the Senate impeachment trial of former president Donald Trump this week are expected to revolve largely around a pair of constitutional questions: A First Amendment defense of his fiery speech ahead of the violent Jan. 6 attack on the Capitol and a challenge to the legality of putting a former president on trial.

Trump is the first president in U.S. history to be impeached twice, and the only one to be tried in the Senate after leaving office. While an impeachment proceeding is distinct from a typical criminal trial, with a different set of rules, Trump’s case will feature broad legal questions about whether his actions violate the Constitution.

Most legal scholars who have studied the issue think post-presidential impeachment and conviction are allowed based on history and past practice in Congress. “The overwhelming scholarly consensus supports this argument,” said Steve Vladeck, a constitutional law professor at the University of Texas School of Law.

A prominent conservative lawyer added political and legal heft to the Democrats’ argument that Trump can be tried in the Senate even after he has left office. The assertion from Republican lawyer Charles J. Cooper in a Wall Street Journal opinion piece published Sunday undercuts the central argument embraced by most GOP lawmakers that it is unconstitutional to convene the Senate trial because Trump is no longer president.

Cooper, who has represented high-profile Republicans and conservative causes in court, said pointedly in his column that because the impeachment power includes the authority to prevent officials from holding future office it “defies logic to suggest that the Senate is prohibited from trying and convicting former officeholders.”

All but five Republican senators previously signaled their support for Trump’s primary line of defense advanced in a January test vote last month by Sen. Rand Paul (R-Ky.). It was not immediately clear whether Cooper’s view, put forward two days before the trial starts, would sway GOP lawmakers.

Senators “should reconsider their view and judge the former president’s misconduct on the merits,” wrote Cooper, who has represented former Trump national security adviser John Bolton, the National Rifle Association and former attorney general Jeff Sessions, a longtime friend.

Vladeck said he doubts Cooper’s backing will change the outcome of the trial. A conviction requires the votes of 67 out of 100 senators in the chamber evenly divided by party.

“Republican senators were gravitating toward this argument [made by Paul] because it allows them to avoid having to condemn or condone what Trump did,” Vladeck said. “It’s a technicality that doesn’t actually have to be correct.”

Vladeck and others have pointed to examples from history, including the impeachment trial of former secretary of war William Belknap in 1876. Belknap resigned just before the House voted to impeach him, but the Senate affirmed its power to hold a trial for the former official, even as it failed to get the two-thirds vote to convict him.

Many Senate Republicans, however, latched on to the constitutional challenge to the process, citing the views of former federal judge J. Michael Luttig, who has argued that only a sitting president can be impeached and tried.

But Luttig on Monday faulted Trump’s legal team for not addressing the particular constitutional question raised by a president being impeached before he left office — but being tried after he departed. “As a consequence, they did not address the arguments that have been made in support of the constitutionality of the Senate trial,” Luttig said.

In response, Trump attorney David I. Schoen said the House managers’ position is that even if the president was impeached after leaving office, it still would be constitutional. The House position, he said, “opens up an absurd Pandora’s box. Who will House Democrats try to impeach next, George Washington?”

In his opinion piece published online Sunday, Cooper takes aim at Republicans who backed Paul’s move last month to dismiss the case as unconstitutional and points to what he calls “the serious weakness of Mr. Paul’s analysis.” The relevant provision of the Constitution “cuts against their interpretation. It simply establishes what is known in criminal law as a ‘mandatory minimum’ punishment: If an incumbent officeholder is convicted by a two-thirds vote of the Senate, he is removed from office as a matter of law.”

Because the Constitution allows the Senate to impose the additional punishment of disqualification from office, Cooper writes, “that punishment can be imposed only on former officers.”

In addition to challenging the process of trying a former president, Trump’s lawyers will argue that his comments attacking the validity of the 2020 election and at the rally before the siege are protected by the First Amendment.

Shortly before the attack on Jan. 6 that resulted in five deaths, Trump, in a rally at the Ellipse park near the White House, called on his supporters to “fight like hell” and to march down Pennsylvania Avenue to stop lawmakers from certifying the election of his rival, President Biden.

Trump’s fiery words to the crowd might not rise to the level of incitement in a traditional courtroom under the First Amendment, constitutional scholars say. But the same legal protections do not apply at an impeachment trial, where Trump is accused of violating his oath as a public official.

There’s a difference between what is impeachable and what is illegal. First Amendment experts distinguished between a political impeachment process and a criminal legal proceeding in a courtroom, where they said it might be difficult to successfully prosecute the president for riling up the crowd before the riot.

The case that Trump’s efforts to subvert the election results and encourage insurrection “contributed to this unprecedented attack on one of the branches of government is strong,” said Suzanne Nossel, chief executive of the nonprofit PEN America who writes about free speech. “You have the president of the United States basically saying, ‘Have at it.’ ”

In impeaching Trump before he left office last month, the House charged the former president with a single count of “inciting violence against the Government of the United States.” The Constitution says the president can be impeached by the House and convicted by the Senate for “high crimes and misdemeanors.”

Trump’s attorneys, Bruce Castor Jr. and Schoen, say Trump was exercising his free speech rights in questioning the election results.

“The attempt of the House to transmute Mr. Trump’s speech — core free speech under the First Amendment — into an impeachable offense cannot be supported, and convicting him would violate the very Constitution the Senate swears to uphold,” Trump’s lawyers wrote in their filing Monday.

But Congress’s power to impeach is not limited to unlawful acts, and the First Amendment does not prevent the Senate from convicting Trump, according to a coalition of more than 100 constitutional law scholars.

“The First Amendment is no defense to the article of impeachment leveled against the former President,” according to a letter circulated by the scholars and first reported by the New York Times. “The president does not have a First Amendment right to incite a mob and then sit back and do nothing as the hostile mob invades the Capitol and terrorizes Congress.”

There are differing views about whether Trump’s speech on Jan. 6 would qualify in court as “incitement to imminent violence” — one of the exceptions to First Amendment protections that allows certain speech to be punished by the government. The key Supreme Court decision in a 1969 case struck down an Ohio law used to convict a Ku Klux Klan leader as too broad. The ruling in Brandenburg v. Ohio created a high bar for finding incitement to protect political speech. The speech or advocacy must be “directed to inciting or producing imminent lawless action” and “likely to incite or produce such action.”

The violence that erupted after Trump’s speech was imminent, but the former president’s language that day could be viewed in court as more ambiguous.

“We fight like hell,” Trump told supporters, “If you don’t fight like hell, you’re not going to have a country anymore.” But early in the speech he also urged them to “peacefully and patriotically make your voices heard.”

Clay Calvert, a professor of law at the University of Florida, said: “Yes, he used the word fight, but he’d say he didn’t use it in a physical sense. It was more implied than explicit. He’d claim he was using that in a fight for your rights situation.” Calvert said it was politically and symbolically wise for Trump to cite the First Amendment defense in part because many conservatives believe free speech is under attack by social media platforms. But ultimately, he said, the defense will have little to no practical effect on the outcome of the impeachment trial because senators are not bound by Supreme Court precedent.