WASHINGTON - The US Senate takes formal steps on Thursday to consider the removal of US President Donald Trump on charges that he abused his power, even as key issues such as whether witnesses will appear at his impeachment trial remain up in the air.The Democratic-led House of Representatives on Wednesday sent two formal charges against Trump to the Republican-led Senate, clearing the way for only the third impeachment trial of a US president to begin in earnest next week.Ceremony, rather than substance, will mark Thursday's proceedings, with the seven House "managers" prosecuting Trump to present the articles of impeachment to the Senate at 12 p.m. (1700 GMT).The Senate will invite US Chief Justice John Roberts to the chamber at 2 p.m. to be sworn in to preside over the trial and, eventually, to swear in all 100 senators. It will then notify the White House of Trump's impending trial.House members voted 228-193, largely along party lines, to give the Senate the task of putting the Republican president on trial on charges of abuse of power for asking Ukraine to investigate political rival Joe Biden and obstruction of Congress for blocking testimony and documents sought by Democratic lawmakers.The Senate is expected to acquit Trump, keeping him in office, as none of its 53 Republicans has voiced support for removing him, a step that requires a two-thirds majority.But Trump's impeachment by the House last month will stain his record and the televised Senate trial could be uncomfortable for him as he seeks re-election. Biden, a former vice president, is a leading contender for the Democratic nomination to challenge him in the Nov. 3 election. Trump denies wrongdoing and has called the impeachment process a sham.A pivotal event leading to Trump's impeachment was a July 25 call in which he asked Ukraine's president to investigate Biden and his son Hunter Biden for corruption and to probe a discredited theory that Ukraine, not Russia, interfered in the 2016 U.S. election.Democrats have called that an abuse of power, saying Trump asked a foreign government to interfere in a US election for his own benefit at the expense of American national security.Trump is also accused by Democrats of abusing his power by withholding $391 million in security aid to Ukraine to pressure Kiev into conducting investigations politically beneficial to him. The money - approved by Congress to help Ukraine combat Russia-backed separatists - eventually was provided to Ukraine in September after the controversy became public.Republicans have argued that Trump's actions did not rise to the level of impeachable offenses. They have accused Democrats of using the Ukraine affair as a way to nullify Trump's 2016 election victory.One bone of contention between Democrats and Republicans has been whether witnesses should appear in the trial, a wild card that could affect public sentiment toward Trump.Democrats will push to hear from witnesses during the trial, something Senate Majority Leader Mitch McConnell has resisted, arguing that senators should consider only the evidence amassed by the House.