The Democrats have lost a series of battles on the first day of Donald Trumpâ€™s impeachment trial, with Republicans voting down attempts to subpoena a cache of documents and witness evidence.
As the third impeachment trial in US history began on Tuesday, senators voted along party lines, 53-47, to block a series of motions from Democratic leader Chuck Schumer.
The dramatic showdown saw his bid to subpoena records and documents from the White House, the State Department and the Office of Management and Budget related to Mr Trump's dealings with Ukraine, fail in the Senate.
Senators also rejected by the same tally a request for a subpoena seeking the testimony of acting White House Chief of Staff Mick Mulvaney.
Democrats have called on the Senate to remove President Trump from office for pressuring Ukraine to investigate former Democratic Vice President Joe Biden, a political rival, and then impeding the inquiry into the matter.
Mr Trump, who was impeached last month by the Democratic-led House of Representatives on charges of abusing power and obstructing Congress, denies any wrongdoing and describes his impeachment as a partisan hoax to derail his 2020 re-election effort.
During early debate, Mr Trump's chief legal defender attacked the case as baseless and a top Democratic lawmaker said there was "overwhelming" evidence of wrongdoing.
With the television cameras rolling, US Chief Justice John Roberts convened the proceedings and the two sides began squabbling over Senate Majority Leader Mitch McConnell's proposed rules for the trial.
White House counsel Pat Cipollone, who is leading Trump's defence, attacked the foundation of the charges against the Republican president and said Democrats had not come close to meeting the US Constitution's standard for impeachment.
"The only conclusion will be that the president has done absolutely nothing wrong," Cipollone said as he argued in favour of McConnell's proposal to decide on whether to allow further witnesses or documents later in the trial.
"There is absolutely no case," he said.
Democratic Representative Adam Schiff, who helped spearhead the House impeachment inquiry, summarised the charges against Mr Trump and said the president had committed "constitutional misconduct justifying impeachment."
Schiff said that although the evidence against Mr Trump was "already overwhelming," further witness testimony was necessary to show the full scope of the misconduct by the president and those around him.
Republican senators have not ruled out the possibility of further testimony and evidence at some point in the trial after days of opening arguments and senators' questions.
But Democrats said they forced Tuesday's repeated votes on evidence and witnesses to get Republicans on the record on the issue.
"This may be our only chance, tonight, to make this a fair trial. And it's just increasingly clear that the White House has no answers for why these documents and these witnesses shouldn't be produced," US Senator Chris Murphy of Connecticut told reporters.
Mr McConnell unveiled a plan on Tuesday to give Democratic prosecutors and Mr Trump's lawyers 24 hours each over three days for opening arguments, easing off an earlier plan to keep them to two days and also allowing the House's record of the probe to be admitted as evidence..
Under Mr McConnell's plan, lawyers for Mr Trump could move early in the proceedings to ask senators to dismiss all charges, according to a senior Republican leadership aide, a motion that would likely fall short of the support needed to succeed.
Even if such a motion fails, Mr Trump is almost certain to be acquitted by the 100-member chamber, where a two-thirds majority is needed to remove him from office. But the impact of the trial on his re-election bid in November is far from clear.
Democrats accuse Trump of pressuring Ukraine to interfere in US elections at the expense of American national security and say he is a danger to democracy. Mr Trump and his legal team said there was no pressure and that the Democrats' case is based on hearsay.