Over the weekend, I finished Lincoln's Constitution by Daniel Farber. The book deals with Lincoln's actions during the civil war and studies their constitutionality. The book's conclusion:

[M]ost of that Lincoln did...was in fact constitutional. He was correct that secession was unconstitutional, a revolutionary act rather than a legitimate exercise of state sovereignty. He was also correct that, in actual areas of war or insurrection, he had emergency power to suspend habeas and impose martial law. This is not to say that everything he did was constitutional. Military jurisdiction was extended beyond constitutional bounds in the North; money was spent and the military expanded without the necessary authority from Congress; and freedom of speech was sometimes infringed. Not a perfect record, but a creditable one, in incredibly trying circumstances.

While I wouldn't call it a page turner, neither was it a book I had to slog through; I looked forward to my time with it. The book is easy for a layman to read and anyone who enjoys Lincoln or constitutional questions (I enjoy both) will find it a good read.