We are hours away - as this is published - from the start of the Trump trial in the Senate. There are links to a number of useful resources in my post of Wednesday 3rd February
It was reported in the Washington Post that the proceedings are likely to begin with debate over whether the Constitution permits the trial of a former President. The Congressional Research Servic discuss the various arguments here. This document has also inbuilt links to a number of documents relevant to the trial.
There are a number of ways to follow the trial - directly and indirectly