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. US Ambassador Sondland to Testify in Trump Impeachment Inquiry VOA News U.S. Ambassador to the E.U. Gordon Sondland on Wednesday will be the most high-profile witness to appear before the U.S. House of Representatives as it holds public hearings on the impeachment inquiry into President Donald Trump. Sondland is set to testify in the morning, followed by career Pentagon official Laura Cooper and Undersecretary of State David Hale Wednesday afternoon. Former White House adviser Fiona Hill and career foreign service officer David Holmes are to testify Thursday. On Tuesday Jennifer Williams, an aide to Vice President Mike Pence, and Lt. Col. Alexander Vindman, the National Security Council's top Ukraine expert, former U.S. Special Envoy to Ukraine Kurt Volker and former NSC official Tim Morrison testified. All nine have testified previously in closed-door hearings about Trump's efforts to pressure Ukraine to investigate his political rival, former Vice President Joe Biden and his son, Hunter, who had served as a board member of a Ukraine natural gas company, and probe a discredited conspiracy theory regarding the 2016 president election. Three of the nine listened in on the July 25 phone conversation between Trump and Ukraine's president. Democrats hope the hearings will sway public opinion in favor of impeachment. Republicans have used them to discredit the impeachment proceedings and poke holes in the witnesses' testimony. Here is what you need to know about the witnesses Wednesday and Thursday and their role in the Ukraine affair. Gordon Sondland As President Donald Trump's ambassador to the European Union, Gordon Sondland was in frequent contact with Trump and other administration officials about Ukraine policy. On July 26, the day after Trump and the Ukrainian president Zelenskiy spoke by phone, Sondland and Trump had their own phone conversation during which the president was overheard asking whether Ukraine would "do the investigation" he had asked for. A wealthy hotel magnate, Sondland gave $1 million to Trump's 2017 inaugural committee. In March 2018, Trump picked him as his ambassador to the European Union. He was confirmed by the Senate in July. Laura Cooper Laura Cooper is a career Pentagon official responsible for policy on Russia, Ukraine and other nations in that region. Cooper first joined the Department of Defense in 2001. She held a series of posts at the Pentagon before being named the deputy assistant secretary of defense for Russia, Ukraine, and Eurasia. In that capacity, she met with Volker in late August to discuss the frozen Ukrainian aid and was told by Volker that the hold might be lifted if Ukraine was willing to issue a statement disavowing election interference and vowing to prosecute anyone engaged in interference. Cooper later told impeachment investigators that she and others had expressed concerns about the legality of withholding congressionally authorized funds for Ukraine David Hale As under secretary of state for Political Affairs, David Hale is the State Department's No. 3 official, a position to which Trump named him in 2018. A graduate of Georgetown University's School of Foreign Service, Hale joined the foreign service in 1984 and holds the rank of career ambassador. In early March, he traveled to Ukraine where he asked then Ambassador Marie Yovanovich to extend her diplomatic term by one year and stay in the country through 2020. Later, when Rudy Giuliani, the president's point man on Ukraine, launched a smear campaign to oust Yovanovitch, Hale instructed a subordinate, George Kent, to "keep [your] head down." Hale testified behind closed doors this month about the State Department's handling of the former ambassador's recall. Fiona Hill A British-born American foreign affairs expert, Fiona Hill served as the National Security Council's top Russia expert until June. The first former White House official to testify in the House impeachment inquiry, Hill told investigators in October that Yovanovitch's removal was the "result of the campaign that Mr. Giuliani had set in motion" and that she had personally been the target of similar smear campaigns. Hill also testified about a July 10 White House meeting between U.S. and Ukrainian officials at which Sondland announced that "we have an agreement with the chief of staff for a meeting (between Trump and Zelenskiy) if these investigations in the energy sector start." David Holmes A career foreign service officer, Holmes has been the political counselor at the U.S. embassy in Kyiv since August 2017. In that capacity, he serves as the senior political and political adviser to the ambassador and has attended many meetings with Zelenskiy and other Ukrainian officials. Holmes is the diplomat who overheard a phone conversation between Sondland and Trump the day after Trump pressed Zelenskiy to carry out corruption investigations. During the call, Holmes testified last week, Trump asked Sondland, "So, he's gonna do the investigation?" According to Holmes' testimony, he heard Sondland reply that "he's gonna do it" and that Zelenskiy would do "anything you ask him to." The account establishes a direct link between Trump and the Ukraine pressure campaign.