Standing in court, the former president pleaded not guilty to charges of financial crimes that he insists are part of a politically motivated witch hunt. Jacob Zuma, once the populist leader of South Africa, cut a humbled figure on Wednesday – and offered a potential glimpse of America’s future.

A similar fate for Donald Trump became significantly more likely with reports that New York prosecutors have convened a grand jury to decide whether to indict him on criminal charges.

The jurists will examine evidence gathered during the Manhattan district attorney’s two-year investigation into the former US president’s business dealings and alleged hush money payments to women on his behalf.

There is a long way to go, but it is a sign that the long arm of the law may reach parts where Congress, in particular the Republican party, consistently failed by holding Trump accountable for his actions.

Prosecutors have a decent chance of maintaining the perception of independence because the decision whether to bring charges rests with a jury of citizens studying evidence in secret rather than with Democrat Joe Biden’s department of justice.

Biden and his attorney general, Merrick Garland, will be sure to stay as far away from the case as possible to avoid any hint of political interference. If the jury goes against him, Trump would be the first former US president charged with a crime.

This would surely produce the trial of the century, a fittingly Trumpian spectacle dominating every screen. Neal Katyal, a former acting solicitor general, told the MSNBC network: “I think it’s a potential sign that it looks like Donald Trump is moving on from the presidency to his next turn on TV, which is as a defendant.”

A criminal conviction and jail sentence would be seen by America’s admirers as evidence of the rule of law – and by its detractors as the vindictive pursuit of a former leader reminiscent of a failing state.

Trump is bound to play on such fears when he soon resumes campaign rallies. He said in a statement on Tuesday: “This is a continuation of the greatest Witch Hunt in American history.”

He added pointedly: “Interesting that today a poll came out indicating I’m far in the lead for the Republican Presidential Primary and the General Election in 2024.”

The fact that the message is tired and predictable makes it no less potent among his core supporters. Special counsel Robert Mueller’s Russia investigation, and the Democrats’ impeachment of Trump over his quid pro quo with the Ukraine, became regular foils for Trump on the campaign trail.

When the rallies resume, expect to hear these golden oldies combined with some new material: how the 6 January insurrection was actually a fun day out with supporters kissing police, only to be hijacked by Antifa; and how the Manhattan district attorney’s case is a Democratic conspiracy designed to thwart any Trump reelection plans.

Prosecutors cannot allow such nonsense to blow them off course; Trump will always find some grievance to weaponise. With the help of rightwing media and an acquiescent Republican party, it might secure him millions of votes but not enough to win the national popular vote and, current polls suggest, not the electoral college.

A Trump 2024 election campaign depends on numerous variables: his age (he turns 75 next month), the lure of the golf course, how Republicans fare in the 2022 midterm elections, whether Republicans produce a viable alternative and how Biden’s economy performs. But the grand jury could scuttle it before it begins.

In America, anything is possible. Four or five years from now, Trump might be back in the White House – or he might be in prison. Only the brave or foolhardy would bet which.