Historic impeachment hearings targeting U.S. President Donald Trump are opening Wednesday in Washington, with lawmakers faced with the question of whether he abused his office to help himself politically.

 Two State Department officials - William Taylor, the current top American diplomat in Ukraine, and George Kent, who oversees Ukraine affairs - are the first witnesses before the House Intelligence Committee in the nationally televised hearings, only the fourth time in U.S. history that an impeachment inquiry has been launched against an American leader.

Taylor and Kent are testifying publicly after weeks of behind-closed-doors hearings.
Top U.S. diplomat in Ukraine William Taylor, arrives to testify before the House Intelligence Committee on Capitol Hill.

Top U.S. diplomat in Ukraine William Taylor, arrives to testify before the House Intelligence Committee on Capitol Hill in Washington, Wednesday, Nov. 13, 2019.

More than a dozen current and former diplomatic and national security officials, including Taylor and Kent, laid out the case in private testimony that Trump temporarily withheld $391 million in military aid to Ukraine to fight pro-Russian separatists in the eastern part of the country unless Ukrainian President Volodymyr Zelenskiy publicly promised to open investigations of one of Trump's chief 2020 Democratic challengers, former Vice President Joe Biden, his son Hunter Biden's work at a Ukrainian natural gas company and a debunked theory that Ukraine worked to undermine Trump's 2016 election campaign.

In the hours ahead of the testimony, Trump railed against the Democratic-led impeachment effort that threatens his three-year presidency, quoting one supporter as noting that he eventually released the U.S. assistance to Kyiv in September without the investigations of the Bidens being opened.

Trump said the witnesses expected to testify about his actions involving Ukraine are "NEVER TRUMPERS!" However, almost uniformly, they are career diplomats and national security officials who have worked for both Republican and Democratic administrations or in the case of one key witness next week, Gordon Sondland, a million-dollar Trump political donor and now the ambassador to the European Union, been appointed by him.