Donald Trump’s indictment in New York on Thursday is a somber watershed in U.S. history. Not only has no former president ever been charged with a crime before, but we are also witnessing the long-overdue reinforcement of a foundational principle of our republic: No one, however powerful, is above the law.

The decision by Manhattan District Attorney Alvin Bragg to indict the former president also illustrates the beauty of the federalism underlying our republic’s design. It is, Supreme Court Justice Louis D. Brandeis wrote, an elegant feature of our federal system that “a single courageous State may, if its citizens choose, serve as a laboratory.”

In this case, it is New York serving as the proving ground to establish the accountability of a man who succeeded in becoming president, in considerable measure, by covering up his past. Some understandably worry that his later attempts to overturn the Constitution were far worthier subjects for indictment. While we wait to see whether charges will be filed on those counts, we should keep in mind that, but for Trump’s alleged misconduct just before the 2016 election, the attempted coup of late 2020 and Jan. 6, 2021, might never have occurred.

Moreover, a prosecutor pursues crimes as he finds them. The precise charges are not yet known, but the case has focused on Trump’s alleged $130,000 payoff to adult-film actress Stormy Daniels to keep her quiet on the eve of the 2016 election — so symbolic of his brand: utter defiance of morality and law in pursuit of power and wealth. If those allegations indeed are the basis of Bragg’s charges, and are proved true, the larger victim will have been the public, from whom crucial information was hidden. Having gotten himself elected, Trump spent four years in office — and all the time since — swinging a wrecking ball against the edifice of our constitutional republic.

Protecting the principle that no person is above the law requires constant vigilance, as we have already come perilously close to losing it once. It was damaged nearly 50 years ago, when another modern president committed provable crimes in office.

In 1974, President Richard M. Nixon escaped criminal accountability for his Watergate offenses when his successor, Gerald Ford, pardoned him to “shut and seal” the book on what he had called “our long national nightmare.” In fact, letting the most notorious political criminal of his day escape justice helped set the stage for the nightmare’s return — with a vengeance. Trump’s misconduct in office exceeded Nixon’s, and he came close to plunging our nation into chaos.

In Federalist No. 1, Alexander Hamilton described the greatest danger to the government that he and his co-founders had designed. The threat came, he wrote, from men who “have begun their careers by paying an obsequious court to the people; commencing demagogues and ending tyrants.” No one in 1787 could have foreseen Trump, but history had taught the founders about the type: men of “perverted ambition” who “hope to aggrandize themselves by the confusions of their country.”

Clarity is the antidote to those confusions. It comes when prosecutors enforce legal lines that separate permissible government action from criminal conduct. Law properly applied has always been the most effective instrument of a stable, constitutionally based society.

We have every reason to expect that Justice Department special counsel Jack Smith and Fulton County, Ga., District Attorney Fani Willis will follow Bragg’s lead with indictments of Trump for breaking far more significant rules that outlaw attempts to negate the people’s will by overturning an election. Indeed, now that Bragg has indicted Trump for getting himself elected via one alleged fraud at the front end of his 2016 election, it would be poetic justice should Smith and Willis indict him later for conspiring to defraud the United States and Georgia, respectively, via a fake-elector scheme at the back end.

Some call it a political mistake to indict Trump. Criminal trial risks making him a martyr, they say, energizing his base in the middle of his campaign for the 2024 Republican nomination. Politics, however, is not the business of prosecutors. Their sworn duty is to follow the facts and enforce the law in their jurisdiction when they have the evidence to prove that the law has been violated.

Trump is entitled to the presumption of innocence, and the case against him must still be argued before a jury of his fellow citizens. Indictment is just the beginning, but it sets this chapter in the timeless story of the law.

What history will note and long remember are two things that happened on March 30, 2023. First, that our federal republic demonstrated that one state could indeed serve as a laboratory — here, to establish a precedent of accountability for the powerful. And second, that an undaunted local prosecutor from that state planted the flag of justice firmly on the side of the rule of law.