Washington: A divided Senate began the impeachment trial of President Donald Trump on Tuesday in utter acrimony, as Republicans blocked Democrats’ efforts to subpoena witnesses and documents related to Ukraine and moderate Republicans forced last-minute changes to rules that had been tailored to the president’s wishes.

In a series of party-line votes punctuating 12 hours of debate, Senate Republicans turned back every attempt by Democrats to subpoena documents from the White House, State Department and other agencies, as well as testimony from White House officials that could shed light on the core charges against Trump.

The debate between the House impeachment managers and the president’s legal team stretched into the early hours of Wednesday in a Senate chamber transformed for the occasion, with Chief Justice John Roberts presiding from the marble rostrum and senators sworn to silence looking on from desks piled with briefing books. It was the substantive start of the third presidential impeachment trial in American history.

Tensions grew so raw that Roberts cut in just before 1am to admonish the managers and the president’s lawyers to “remember where they are” and return to “civil discourse”.

“They are addressing the world’s greatest deliberative body,” he said.

On its face, the prolonged debate was about the rules and procedures. But it set the stage for a broader political fight over Trump’s likely acquittal and will help shape the 2020 campaign.

Conflicting claims

Democrats were laying the groundwork to argue that the trial was rigged on Trump’s behalf and to denounce Republicans — including the most vulnerable senators seeking reelection — for acquiescing. Republicans, for their part, insisted that the Senate must move decisively to remedy what they characterised as an illegitimate impeachment inquiry unjustly tarring the presidency.

Standing in the well of the Senate, the Democratic House impeachment managers urged senators to reject proposed rules from the majority leader, Sen. Mitch McConnell of Kentucky, that would delay a debate over witnesses and documents until the middle of the trial, with no guarantee that they would ever be called.

“If the Senate votes to deprive itself of witnesses and documents, the opening statements will be the end of the trial,” said Rep. Adam Schiff of California, the lead manager. He said McConnell’s proposal was tantamount to saying, “Let’s have the trial, and maybe we can just sweep this all under the rug.”

But Republicans were unpersuaded and, just before 2am. Eastern, voted along party lines, 53-47, to ratify McConnell’s trial plan. As adopted, the resolution would pave the way for oral arguments against Trump to begin as soon as Wednesday.

They rejected 10 other amendments by the same margin. An 11th Democratic proposal, to lengthen the timetable for the prosecutors and defence to file trial motions, gained the support of one Republican, Susan Collins of Maine, but still failed.

At the heart of the trial are charges of abuse of power and obstruction of Congress approved last month by the Democratic-led House. They assert that Trump used the power of his office to pressure Ukraine to announce investigations into his political rivals, withholding as leverage nearly $400 million (Dh1.5 billion) in military aid and a White House meeting. The president then sought to conceal his actions from Congress, the charges say, by blocking witness testimony and documents.

Trump’s legal team argues that the charges are baseless and amount to criminalising a president’s prerogative to make foreign policy as he sees fit. In a break with most constitutional scholars, they also claim that the impeachment was unconstitutional because the articles of impeachment do not outline a specific violation of a law.

But on Tuesday, the debate focused principally on what would constitute a fair trial.

“This initial step will offer an early signal to our country,” McConnell said before it got underway. “Can the Senate still serve our founding purpose?”

McConnell also received a sharp reminder about the limits of his power to control an inherently unpredictable proceeding.

Under pressure from Republican moderates, he was forced to make some last-minute changes to the set of rules he unveiled Monday, which would have squeezed opening arguments by both sides into two 12-hour marathon days. McConnell’s rules also would have refused to admit the findings of the House impeachment inquiry into evidence without a separate vote later in the trial.

The compressed timetable was in line with a White House request to quickly dispense with opening arguments so that Trump’s team could complete his defence before the weekend.

Collins, Rob Portman of Ohio, and Lisa Murkowski of Alaska, among others, objected privately to those provisions, which they believed departed too much from procedures adopted unanimously for the 1999 trial of President Bill Clinton and could further expose Republicans to accusations of unfairness.

The objections were raised at a closed-door luncheon just before the trial was to begin, according to aides familiar with the conversation. McConnell rushed to submit a revised copy of the resolution — with lines crossed out and changes scrawled in pen in the margins — when it was time for the debate.

When the resolution was read aloud on the Senate floor, two days had been extended to three and the House’s records would be automatically admitted into evidence, although McConnell inserted a new provision that would allow Trump’s team to move to throw out parts of the House case.

The last-minute reversal underscored the influence of a small group of moderate Republicans in the narrowly divided Senate whose interests and demands could prove decisive in a more formal debate over witnesses and documents to come.

Trump in Davos

Half a world away, Trump sought to use the global stage at the World Economic Forum in Davos, Switzerland, to project confidence about his standing at home. He swatted away questions from reporters about the trial, instead bragging about the strength of the American economy under his leadership.

But in the Senate chamber, Trump’s lawyers replayed many of his most frequent and personal grievances, accusing Democrats in only slightly more lawyerly terms of conducting a political search-and-destroy mission.

“It’s long past time that we start this so we can put an end to this ridiculous charade and go have an election,” said Pat Cipollone, the White House counsel.

Democrats, who came armed with digital slides and video clips to drive home their arguments, spent hours detailing the factual record compiled by the House investigation and cataloguing the witnesses and thousands of pages of highly relevant documents Trump had succeeded in withholding. Senators facing such a grave decision as removing a president, they argued, have a responsibility to try to push all the facts to light.

“With the backing of a subpoena authorised by the chief justice of the United States, you can end President Trump’s obstruction,” said Rep. Zoe Lofgren of California, the first woman in history to speak on the Senate floor as an impeachment manager. “If the Senate fails to take this step, you won’t even ask for the evidence. This trial and your verdict will be questioned.”

Just an hour or so before the trial began, the seven House managers submitted one final written rebuttal to arguments put forward against their charges by Trump’s lawyers. In 34 pages, they rejected the lawyers’ assertion that abuse of power was not an impeachable offence and that Trump had acted legally when he ordered administration officials not to appear for questioning in the House or provide documents for the impeachment inquiry.

Locked in silence for much of the day, senators were able to talk only before the proceeding began or during brief breaks. Speaking to reporters on Tuesday morning, Sen. Chuck Schumer of New York, the Democratic leader, denounced McConnell’s rules as deeply unfair and skewed toward Trump.

“It is completely partisan. It was kept secret until the eve of the trial,” he said. “The McConnell rules seem to have been designed by President Trump and for President Trump, simply executed by Leader McConnell and Senate Republicans.”

Inside the chamber, Schumer forced votes on demanding documents and compelling testimony from four current and former Trump administration officials who were blocked from speaking with the House: John Bolton, the former White House national security adviser; Mick Mulvaney, the acting White House chief of staff; Robert Blair, an adviser to Mulvaney; and Michael Duffey, a White House budget official.

Each time, McConnell moved to kill the proposal before it could be considered and was sustained by unified Republican support. At one point, he offered to short-circuit the debate to speed up the votes, but Democrats who want a full account of Trump’s blockade on record declined.

“This is the fair road map for our trial,” McConnell declared. “We need it in place before we can move forward.”