Since 2016, a genre of journalism has emerged in the Democratic press to explain the 45th American president as a version of one of history’s great tyrants. There is, of course, Trump as Hitler, bolstered by a tidbit in a recent book that President Trump once complained that his generals were not as obedient as those in Nazi Germany. 

The House majority whip, Jim Clyburn, has compared Mr. Trump to an Italian fascist, Benito Mussolini. Comedy writer Larry Wilmore in 2017 dubbed Mr. Trump “Orange Julius Caesar.” My fellow scribes, though, would be better off likening Mr. Trump to an ancient Roman populist, Tiberius Gracchus.

Like Mr. Trump, Tiberius was born to wealth and in his political career betrayed his elite caste. Tiberius proposed the first agrarian reform laws for the Roman republic that would transfer land owned by the state to the landless plebeians.

Mr. Trump campaigned on ending complex multilateral trade deals that he said robbed the working class of quality jobs and economic security. Also like Mr. Trump, Tiberius violated the norms of his era. In the case of Tiberius, the trouble starts with his term as tribune.

In Republican Rome, the office of the tribune was elected by the plebeian caste and presided over the people’s assembly, which was counterbalanced by the Roman senate, whose members came from the aristocracy. Another tribune, named Marcus Octavius, bribed by wealthy senators, vetoed the Gracchus reforms.

Tiberius then took the unusual step of rallying a vote to impeach Octavius, something that had never been done before to a tribune. He also had his men lay hands on his rival and physically removed him from the assembly.

After that, Tiberius wielded his own veto over routine matters necessary for the functioning of the Roman state, to pressure the senate to pass his reforms. Eventually, the senate relented and Tiberius won.

Tiberius though was not finished. After his victory, he announced his intention to run for a second consecutive term as tribune, another norm violated for the Roman republic. He also proposed that lands and wealth bequeathed to Rome by the king of Pergamum fund his agrarian reforms for the plebeian class. The Roman senate before this had exclusive power of foreign policy. A faction of senators seethed in anger.

Mr. Trump is also a norm violator. He is the first modern president not to release his tax returns. He attempted to pressure the president of Ukraine, Volodymor Zelensky, to announce an investigation into a political rival’s son.

Plus, Mr. Trump fired the FBI director in the middle of his 10-year term. Mr. Trump would often announce important policy decisions by tweet. The former president, of course, did not accept the results of the 2020 election and still doesn’t to this day.    

Nor is Mr. Trump’s story finished. Yet in the demise of Tiberius, a lesson lurks for the American republic. As votes were counted for the second and unprecedented election of Tiberius, a Roman senator and high official named Publius Cornelius Scipio Nasica pleaded with the Senate that Tiberius wanted to be king and would destroy the republic.

So Nasica gathered a mob of fellow senators and their aides and rampaged against Tiberius and his allies at the nearby people’s assembly. The mob killed Tiberius and dumped his body in the Tiber River.

Plutarch, the historian of Rome, wrote that the murder of Tiberius and his supporters was “the first sedition at Rome, since the abolition of royal power, to end in bloodshed and the death of citizens.” It would not be the last.

The death of Tiberius marked the beginning of the end for the Roman republic. Violence became an acceptable means of settling political disputes. In less than a century, Julius Caesar would rise to become a de facto emperor and the Roman senate would be reduced to a debating society.

Something similar may be happening in respect of Mr. Trump. No past president has ever been criminally indicted. Even if Attorney General Garland believes he has a winning case against the former president on obstruction, he would be, by going ahead, setting a precedent. This may not introduce a cycle of political violence in America, but it would open the door to prosecuting future past presidents.

Democrats will argue that the risk to the justice system is worth it if Mr. Trump can be disqualified from running for president in 2024. Saving the republic from an authoritarian demagogue is too important. Well, Nasica believed the same thing. He argued that murdering Tiberius would save the Roman republic from tyranny. Instead of saving the republic, Nasica planted the seeds for its demise.