NEW YORK — His caseload has featured charges against former President Donald Trump’s company and some of Trump’s closest associates in business and politics.Now Judge Juan Manuel Merchan is poised to take the historic hush-money prosecution of Trump himself.Merchan, a former prosecutor with 16 years on the bench, was expected to preside Tuesday over the unprecedented arraignment of a former U.S. commander in chief. Trump will appear to answer charges arising from a grand jury investigation into payments …