With 53 Democrats and 47 Republicans currently in the Senate, four Republicans and all Democrats will have to vote for witnesses to continue the process. Republican Senator Susan Collins, from Maine, and Mitt Romney from Utah have both said they will vote for a witness statement, while Republican Senator Lamar Alexander from Tennessee has said he won't. Lisa Murkowski from Alaska is still undecided.
If it is a 50-50 split, the decisive vote may fall on John Roberts, supreme judge of the Supreme Court, who oversees the trial, which runs six days a week, including Saturdays.
If no witnesses are called, it is possible that there will also be a vote on Friday on whether or not to condemn the president, possibly ending the trial.
Democrats fish to call on former national security adviser John Bolton to testify. In a manuscript for his upcoming book that was revealed on Sunday by The New York Times, Bolton writes that Trump said he would withhold $ 391 million in military aid from Ukraine unless the country announced an investigation into its political rivals.
The issue is whether Trump should be removed from office because of his behavior in dealing with Ukraine. That includes a phone call in July in which he appears to be asking the country's new president to investigate former US vice-president Joe Biden, currently a democratic presidential candidate, and his son Hunter Biden's ties with a Ukrainian gas company.
In a December vote, the House approved two articles of accusation accusing Trump of abusing power and obstructing Congress. Both votes were largely along party lines in the Democratically controlled House. The votes of 67 senators in the senate controlled by the republicans are required to put the president out of office.
Full coverage of the charge test can be found on CBS News here.
How can I watch?
Different news networks and outlets will stream the events of the day. A number of broadcasters, including PBS and cable news channels Fox News, MSNBC, CNN and C-SPAN, have pre-programmed regular programming to offer live broadcasts. (Disclosure: CNET is a division of CBS Interactive, owned by ViacomCBS.)
Local broadcasters CBS, ABC and NBC have also banned regular programming for broadcasting the trial.
You can also test the live online streaming for free on sites such as C-SPAN or via YouTube channels for various news channels, including CBS News, which are included above.
What time does it start?
The Senate trial on Friday starts at 10 a.m. PT / 1 p.m. ET
Who else has been dropped off?
Trump is the third president to be deposed by the House since the constitution was adopted in 1788. President Andrew Johnson and Bill Clinton were also deposed.
President Richard Nixon resigned before the House had the opportunity to accuse him of his role in the Watergate scandal. Both Johnson and Clinton were acquitted by the Senate in their respective deposition sentences.
What does Trump have to say?
In a six-page letter to House Speaker Nancy Pelosi in December prior to the House vote, Trump destroyed the procedure and said, "more appropriate trial was offered to those accused in the Salem Witch Trials. "
"It is time for you and the very partisan Democrats in Congress to immediately stop this accusation fantasy and go back to work for the American people," wrote the president. "Although I don't expect you to do that, I am writing this letter to you for the purpose of history and to place my thoughts on a permanent and indelible report."
He has since responded and shame " and a " hoax ." While the conversation started over the weekend for former national security adviser John Bolton to testify, Trump tweeted Monday that he had never told Bolton & # 39; to help Ukraine to investigate.about the accusation, calling it a "
Bolton writes in his new book, the design of which was described to The New York Times, that Trump refused. Release $ 391 million in military aid unless Ukraine helped investigate its political rivals.
Where can I find out more about deposition?
CBS News has full coverage of the deposition process, investigation and procedures.
Originally published on November 12 and regularly updated.
Correction, November 14: An earlier version of this story incorrectly describes Joe Biden. He is a democratic presidential candidate.