Much of his writing on Stalinist Soviet Union is based on newly released archival documents, including personal correspondence, drafts of Central Committee paperwork, new memoirs, and interviews with former functionaries and the families of Politburo members.
Kebanyakan tulisannya tentang Uni Soviet Stalinis berdasarkan pada dokumen-dokumen arsip yang baru dirilis, termasuk korespondensi pribadi, rancangan kertas kerja Komite Pusat, memoir baru, dan wawancara dengan para bekas fungsioner dan keluarga anggota Politbiro.