Impeachment is not an anti-Trump screed, nor is it a dry dissertation on Constitutional law. Sunstein's book is an engaging exploration of the impeachment clause of the US Constitution, what the framers of the Constitution were thinking when they wrote it and how it has been interpreted over the years.
Having just rebelled against a monarchy, many of the attendees of the Constitutional Convention were apposed to any sort of executive leader. As a compromise a system was created to remove the President from office, but the system had to be difficult enough that impeachment did not become a tool of partisan fighting. Which is not to say that it has not been used for that purpose, see the Clinton impeachment. Policy disagreement, general incompetence, and being a public embarrassment to the nation are not grounds for impeachment. Some actual crimes committed by the President do not rise to the level of impeachment, but some actions that are not legally crimes can qualify as impeachable offenses. The author also explores the 25th amendment, which added another way of removing the President from office based on incapacity, and in turn raised many more questions.
Although the name Trump is never mentioned in the book, the timeliness of its subject causes the current President to loom of the discussion. It increasingly appears that within the next few years we will witness another impeachment proceeding with more merit behind it than the last one. I recommend this book as an excellent and very readable overview of the history and legal thought behind impeachment and why it must not be invoked frivolously but must be invoked when there is just cause.