Senators have taken oaths to act as impartial jurors in a trial presided over by US Chief Justice John Roberts. House Democrats known as "impeachment managers" act as the prosecution, while Mr Trump's legal team acts as the defence. Under the rules approved by the Republican majority after a first day of proceedings that finished close to 02:00 local time (07:00 GMT), each side will be given up to 24 hours to lay out their case in opening arguments, over three days. Senators are barred from live tweeting and from speaking to those sitting near them while the case is being heard. No outside reading materials are allowed to be brought in. Opening arguments will begin on Wednesday afternoon. After this finishes, probably early next week, senators will have a chance to ask questions. They have been given 16 hours. Then attention will return again to the key issue of new witnesses and evidence. Democrats want to hear from key White House aides who worked closely with Mr Trump, including acting Chief of Staff Mick Mulvaney and Mr Bolton. Republicans have so far blocked their attempts. How were Democrats blocked on Tuesday? By party-line votes of 53-47, the Senate rejected a series of Democratic bids to obtain documents and evidence in the impeachment trial. Senators blocked a motion from Democratic leader Chuck Schumer to subpoena White House files related to Mr Trump's dealings with Ukraine. They also rejected follow-up motions demanding a subpoena of records and documents from the state department and White House budget office. Republican Senators turned back an effort by Democrats to subpoena Mr Bolton, who has said he would comply with any such order. In his opening statement, Adam Schiff, the House Democrat leading the impeachment case, said most Americans "do not believe there will be a fair trial". "They don't believe the Senate will be impartial," he said. "They believe the result is pre-cooked." The president's legal team had earlier demanded he be immediately acquitted, calling the trial "a dangerous perversion of the constitution". At one point during bitter arguments, Justice Roberts admonished both the House prosecutors and the Trump legal team, asking them to remember that they were "addressing the world's greatest deliberative body". How did Mitch McConnell come under pressure? Backed by the president's lawyers, Senate Majority Leader Mitch McConnell had initially planned to condense the opening arguments from three days to two. Democrats said this would have been no less than a cover-up. But after a meeting with senators, including some Republicans, Mr McConnell agreed on Tuesday to three days for opening arguments. The senators had expressed concern about how middle-of-the-night sessions would look to US voters. But White House Counsel Pat Cipollone, the president's lead lawyer, had called the plan "a fair process". Several more days of procedural tangles are expected. What are the charges? First, the president is accused of seeking help from Ukraine's government to help himself get re-elected in November. It is claimed that, during a call with Ukrainian President Volodymyr Zelensky, he held back military aid as he sought an anti-corruption investigation into Democratic White House candidate Joe Biden, whose son, Hunter, held a board position with a Ukrainian energy firm, Burisma. The second allegation is that, by refusing to allow White House staff to testify at the impeachment hearings last year, Mr Trump obstructed Congress. The Senate is hearing the case as the Democratic-led House voted to impeach Mr Trump on 18 December.