Donald J. Trump, the 45th president of the United States, was charged this week by federal prosecutors with conspiring to defraud the United States, obstructing official proceedings and undermining his country’s democracy.

While this is neither the first, nor likely the last of Trump’s legal problems — he already faces four other cases in state and federal courts and at least one more indictment is expected — this is the most serious and important of those proceedings.

The case against Trump is a test for the rule of law in the U.S. It will show whether all are equal in the eyes of the American justice system and whether it can hold accountable an individual who has no regard for the norms that have governed political life in the country and society itself. Its implications extend far beyond the future of Trump. It is a test of U.S. democracy.