Legitimate use of unilateral authority - and book suggestions

[T]here were dramatic increases in the size of the army and navy, all accomplished by presidential decree. This was arguably contrary to the clearly expressed congressional power "to raise and support armies." However, the president has unilateral authority to federalize the state militias when he believes a crisis calls for this. Lincoln thus took a legitimate step when on April 15 he declared the existence of a sufficient state of emergency and called up seventy-five thousand members of state militias into national service.

The Unitary Executive

S. G. Calabresi, C. S. Yoo

The Unitary Executive offers a vivid account of the historical and legal foundations of the wide presidential powers of the Chief Executive of the United States. Understanding it is to understand the expansion of executive powers in all governments and nations in the post-Enlightenment world, as well as the exercise of unilateral authority elsewhere.

What are your book suggestions for May (on any subject whatsoever)?