"Because he can." 

That's the answer one has to give to those who ask how Alvin Bragg, a local district attorney in office by the slimmest of margins—and then only because of a huge subsidy from the anti-American billionaire George Soros—can get away with antics like indicting Donald Trump, a former (and, possibly, future) president of the United States, and, now, with charging former Marine Daniel Penny with manslaughter because he (along with at least two others) intervened to stop Jordan Neely from attacking fellow passengers on a New York subway. 

Because he can. As a friend remarked when digesting the spectacle of Penny being led away in handcuffs, totalitarian movements often start slowly, almost timidly, but as they gain power, they become more brazen. After a certain point, they do outrageous things just to intimidate the public and demonstrate their power.  

We now know that the FBI, the CIA, and other elements of America's security apparatus intervened directly in the decision making of Twitter and other social media companies to influence the course of the 2020 election. One part of that intervention had to do with organizing 51 senior former intelligence figures to sign a letter declaring that Hunter Biden's laptop was "Russian disinformation." That was a lie. They knew it was a lie. It didn't matter. They did it because they knew they could get away with it.