Works of fiction that purport to be collections of documents—let’s call them “assemblage novels”—are hard to pull off. The Scottish writer Graeme Macrae Burnet succeeded in 2015—and ended up on the Booker Prize shortlist—with His Bloody Project, a novel that was supposedly a collection of documents relating to a 19th-century murder. Max Brooks’s Zombie Survival Guide, a clever fake manual for enduring the zombie apocalypse, is another recent entry in the genre. Now comes Jeffrey Lewis, an arms control expert at the Middlebury Institute of International Studies and a prolific tweeter (he’s @armscontrolwonk), and his 2020 Commission Report on the...