text: Weeks of private testimony have unearthed credible evidence that President Donald Trump withheld American military aid to pressure besieged Ukraine to investigate his political rivals, including former Vice President Joe Biden. As the House’s impeachment inquiry moves into a public phase with televised hearings beginning Wednesday, Democrats must focus on the central issue in any impeachment proceeding - the president’s conduct - and provide the clearest, most concise picture possible so Americans can reach their own conclusions about Trump’s conduct and whether he should be removed from office.
  
  The House is leading off with three witnesses centrally involved in U.S. dealings with Ukraine who are expected to bolster the core complaint against the president - that he held back military aid Ukraine desperately needed to fight Russian-backed separatists in an attempt to pressure the country’s new president to publicly pledge to investigate the business dealings of Biden’s son in Ukraine and the discredited theory that Ukraine meddled in the 2016 election to help Hillary Clinton.
  
  A whistle-blower complaint about a July 25 call between Trump and Ukraine’s president resulted in House Democrats opening the impeachment inquiry and moving methodically to this point. According to a reconstructed transcript released by the White House, Trump asked Ukraine’s leader “to do us a favor” by opening the investigations. The president and congressional Republicans have tried to make the whistle-blower’s identity and motivations the issue. But Trump’s attempt to extort a foreign government speaks for itself. The whistle-blower’s initial complaint has been largely corroborated and expanded upon by multiple senior U.S. officials, including an Army colonel on the National Security Council who listened in on the call and reported his concerns to his superior.
  
  The House Intelligence Committee will hear Wednesday from William Taylor, the top American diplomat in Ukraine, who in his private testimony described the leverage to be had from the grave consequences in holding up nearly $400 million in military aid to Ukraine amid its proxy war with Russia. It will also hear Wednesday from George Kent, a senior State Department official who raised alarms over what he saw as a politically motivated prosecution and a hijacking of U.S.-Ukrainian policy by Trump’s personal attorney and fixer, Rudy Giuliani. On Friday, Marie Yovanovitch, the former U.S. ambassador to Ukraine, is expected to discuss an Oval Office smear campaign that led her to being recalled earlier this year. These are credible witnesses whose integrity cannot be dismissed by Trump’s serial tweeting.
  
  As the public impeachment hearings get under way, an even richer picture of this scandal may be forthcoming. A Giuliani associate indicted on campaign finance charges last month is preparing to meet with investigators to give his account of the Ukraine story. The president’s former national security adviser, John Bolton, who referred to Giuliani as a “hand grenade” and worked feverishly to cut him out of the loop, has hinted he has “relevant” conversations to share. And Gordon Sondland, a Trump campaign donor who became the White House’s key envoy to Ukraine, recently revised his earlier testimony to House investigators, acknowledging that he made clear to Ukrainian leaders “that resumption of the U.S. aid would likely not occur” until that country committed publicly to investigating the Bidens. Facts are indeed stubborn things -- even in an era when the nation’s president has so little regard for them.
  
  The House must not allow these public hearings to become a political circus. The president’s apparent attempt to extort a foreign government for his own political gain is the issue, not who first brought it to public attention. The House should follow the facts, present a coherent picture of what happened and establish a credible basis for Congress to decide whether to impeach.
  
  Editorials are the institutional voice of the Tampa Bay Times. The members of the Editorial Board are Times Chairman and CEO Paul Tash, Editor of Editorials Tim Nickens, and editorial writers Elizabeth Djinis, John Hill and Jim Verhulst. Follow @TBTimes_Opinion on Twitter for more opinion news.