The criminal tax fraud trial of Donald J. Trump’s family real estate business hinged on endless rows of spreadsheets and tax documents bristling with indecipherable numbers. Now a jurist with 16 years on the bench, he oversaw the only consequential criminal trial to date involving the former president. The case enraged Mr. Trump and his supporters and could permanently damage the business and influence the 2024 presidential campaign. During the five-week trial, the gray-haired Justice Merchan maintained an order that is often lacking elsewhere in state court in what can be a rough-and-tumble practice of criminal law. Finally, Justice Merchan made a frustrated gesture for the defense and prosecution to approach the bench.