The end of the Senate impeachment trial is drawing near with an unpredictable day ahead. First, the Senate will debate for four hours on whether to call new witnesses to trial. Then, they will take a vote on the witness question. After that, Senators could put forward new motions to extend debate on the Senate floor into the days ahead, or they could move quickly to a final vote on the two articles of impeachment today.

Frank Thorp, NBC News producer covering the Senate, lays out what to expect.

For a transcript, please visit https://www.nbcnews.com/articletwo.