By Jack Queen, Luc Cohen and Joseph Ax

NEW YORK, May 14 (Reuters) -

Donald Trump's former fixer Michael Cohen will resume testifying on Tuesday at the Republican presidential candidate's criminal trial, a day after telling jurors that Trump personally authorized him to make a hush money payment to a porn star weeks before the 2016 election.

Cohen, once so loyal to Trump that he claimed he would take a bullet for his boss, is the prosecution's most important witness. In hours of testimony on Monday, he said Trump ordered him to pay the adult film actress Stormy Daniels - "Just do it," Cohen remembered Trump saying - to ensure her silence about an alleged 2006 sexual encounter.

Cohen's $130,000 payment in October 2016 is at the heart of Trump's trial, the first for a former U.S. president, which began in New York state criminal court in Manhattan a month ago.