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:FILE – Former national security adviser John Bolton gestures while speakings at the Center for Strategic and International Studies in Washington, Sept. 30, 2019.For the DemocratsJohn Bolton, former national security adviser. He is perhaps the most sought-after of all witnesses on the Democrats’ list. Democrats say he has direct knowledge of efforts led by Trump’s private lawyer, Rudy Giuliani, to get Ukraine to investigate the Bidens in exchange for U.S. military aid and a White House meeting between Trump and Ukrainian president Volodymyr Zelenskiy. Bolton, according to a former aide, once called Giuliani a “hand grenade who is going to blow everybody up,” and denounced the Ukraine pressure campaign as a “drug deal.”Mick Mulvaney, acting White House chief of staff. As a member of Trump’s inner circle, Mulvaney is a witness to events at the heart of the impeachment case. Democrats say Mulvaney was a “central figure” in Trump’s pressure campaign against Ukraine, and played a key role in carrying out the president’s order to freeze military aid to Ukraine. Mulvaney defied a subpoena to testify.  However, he admitted during an October press conference that the administration had withheld the aid to pressure Ukraine, but he walked back his statement, insisting there had been no “quid pro quo.”
Robert Blair and Michael Duffey, senior White House officials. Serving one rung below Mulvaney, Blair and Duffey are the two officials who were tasked with relaying Trump’s order to freeze the military aid to other administration officials. On June 19, the day after the Pentagon announced $250 million in military aid to Ukraine, Blair, a senior adviser to Mulvaney, emailed the head of the Office of Management and Budget. “We need to hold it up,” Blair said. The same day, Duffey, an OMB associate director, emailed a Pentagon official. “The president has asked about this funding release,” Duffey said.FILE – Then-Vice President Joe Biden and his son Hunter are pictured at a college basketball game in Washington, Jan. 30, 2010.For the RepublicansHunter Biden. Throughout the impeachment process, Republicans have said his involvement with Burisma Holdings, a Ukrainian natural gas company with a reputation for graft, would validate Trump’s call for investigations into corruption. Democrats have rebuked the call as an attempt to shift attention from Trump’s misconduct.Joe Biden. Trump and his allies have alleged that Biden, while serving as vice president and the Obama administration’s point man for Ukraine policy, got Ukraine’s top prosecutor fired in order to block an investigation of Burisma and protect his son’s lucrative position at the company. Last month, Biden said he would testify if subpoenaed. However, following a report that Democrats were mulling asking either Biden to testify in exchange for Bolton’s testimony, the former vice president said Wednesday he would not take part in a witness swap.Burisma board member Devon Archer; the unidentified intelligence officer who filed a whistleblower complaint at the heart of the impeachment proceedings; and Alexandra Chalupa, a Ukrainian American operative for the Democratic National Committee, who is at the center of a conspiracy theory pushed by Republicans that it was Ukraine, not Russia, that meddled in the 2016 U.S. presidential election. 
 
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