Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. Fight Intensifies Over Calling Witnesses for Trump's Impeachment Trial Masood Farivar WASHINGTON - As the impeachment trial of President Donald Trump grinds on after a bitter fight over rules, the two sides in the high-stakes proceeding are bracing for another round of partisan bickering over a deeply divisive issue: witnesses. Democrats have a list of four witnesses they say could fill in the blanks in the impeachment case against Trump. The four officials refused to testify for different reasons during the House inquiry that led to Trump's impeachment on abuse of power and obstruction of Congress. At the top of the list is former National Security Adviser John Bolton, who has said he would testify if subpoenaed. On the Republican side, most senators remain opposed to calling additional witnesses, saying the House Democrats' case against Trump should rise or fall on the 17 witnesses who cooperated with the impeachment inquiry. But if Democrats should somehow prevail in calling Bolton and others to the Senate trial, Republicans have a coveted witness of their own: Hunter Biden, son of former Vice President Joe Biden. With control of only 47 of 100 seats in the Senate, the Democrats would have to persuade four moderate Republicans to side with them in order to call witnesses in the coming week and greatly expand the scope of the proceedings. Ultimately, any additional testimony is unlikely to sway public opinion or make a difference in a trial whose outcome has long been deemed a foregone conclusion. " I think most of us have had enough evidence," said Mark Graber, a constitutional law professor at the University of Maryland. "I'm ready to vote. I think most people are ready to vote." Here is a look at the witnesses both sides want to hear from: .