After US Chief Justice John Roberts convened the proceedings, the two sides began more than 12 hours of squabbling over Senate Majority Leader Mitch McConnell's proposed rules for the trial
The Republican-controlled US Senate voted on Wednesday on party lines to approve the rules for President Donald Trump's impeachment trial, rejecting Democratic efforts to obtain evidence and ensure witnesses are heard.
As the third presidential impeachment trial in US history began in earnest, Trump's chief legal defender argued the Democratic case was a baseless effort to overturn the 2016 election but a top Democratic lawmaker said there was "overwhelming" evidence of wrongdoing.
Trump was impeached last month by the House of Representatives on charges of abuse of power and obstruction of Congress for pressuring Ukraine to investigate former Democratic Vice President Joe Biden, a political rival, and impeding the inquiry into the matter. The president denies any wrongdoing.
After US Chief Justice John Roberts convened the proceedings, the two sides began more than 12 hours of squabbling over Senate Majority Leader Mitch McConnell's proposed rules for the trial.
Senators voted along party lines, 53-47, to block four separate motions from Democratic leader Chuck Schumer to subpoena records and documents from the White House, the State Department, the Defence Department and the Office of Management and Budget related to Trump's dealings with Ukraine.
By the same tally, senators also rejected requests for subpoenas seeking the testimony of acting White House Chief of Staff Mick Mulvaney, former national security adviser John Bolton, White House aide Robert Blair and White House budget official Michael Duffey.
Under McConnell's hastily revised set of procedures for the trial, there will be 48 hours of opening arguments - 24 hours for each side - over six days, easing off an earlier plan to keep them to two days each. It also allows the House's record of the probe to be admitted as evidence.
The arguments were scheduled to begin when the trial resumes at midnight Dhaka time on Thursday. The Senate trial is expected to continue six days a week, Monday through Saturday, until at least the end of January.
Republican senators have not ruled out the possibility of further testimony and evidence at some point after opening arguments and 16 hours of senators' questions, but they held firm with Trump's lawyers to block Tuesday's Democratic requests for witnesses and evidence - a potentially good sign for the White House.