The historical reckoning of most modern presidents goes through several seasons, but it’s been a long, cold winter for Richard Nixon. During the 40 years since he left office, his legacy has been defined solely by the Watergate scandal that led to his resignation.

The same Oval Office recordings that were so crucial in establishing Nixon’s involvement in the Watergate cover-up, says historian Douglas Brinkley, are beginning to thaw his reputation on matters of foreign policy. Brinkley is co-editor with Luke Nichter of The Nixon Tapes: 1971-1972, the first of an ambitious two-volume collection of Nixon’s Oval Office recordings published just ahead of this week’s 40th anniversary of Nixon’s resignation from office on August 9, 1974.

Brinkley, who has written books about Teddy Roosevelt, Gerald Ford, and Jimmy Carter, and edited The Reagan Diaries, talked to The Daily Beast about what the Nixon tapes will mean for historians’ assessments of the 37th president...