Cook Political Report’s Jennifer Duffy had an interesting survey of the 2016 Senate election landscape, linking the unpredictability of the primary process with forecasting the fall’s Senate elections. Even if—as now seems likely—Hillary Clinton comfortably wins, Duffy noted examples of the losing party doing OK in Senate elections, pointing to 1964, 1972, 1984, 1996, and 2000. (The 1996 races deserve more attention from both political analysts and historians, since the GOP’s key victories came, counterintuitively, in moderate states—Oregon, New Hampshire, Maine—or in Clinton’s Arkansas.) The first three years Duffy deemed “lonely landslides,” with LBJ, Nixon, and Reagan winning overwhelming victories but their parties having middling (or worse) performances in the year’s Senate races.

These three “lonely landslides” seem to me quite different. 1972 definitely was such a phenomenon—liberal Democrats captured GOP seats in South Dakota, Maine, Colorado, Iowa, and Delaware. 1984 was murkier—Democrats gained seats, but there were relatively few Republican pickup chances after a good year for the GOP in 1978. And Reagan’s margin certainly carried Mitch McConnell to victory in Kentucky, probably accounted for Jesse Helms’ win in North Carolina, and ensured that seats of some GOP freshmen (New Hampshire, Maine, Colorado) never became competitive. Finally, in the Exon-Hoch contest in Nebraska, it produced the 1980s equivalent of the 2014 Warner-Gillespie race in Virginia—a near-upset of enormous proportions in a race that had attracted scant attention before Election Day. In short, unlike Nixon in 1972, Reagan’s coattails affected the Senate elections.

1964, on the other hand, shouldn’t be considered a “lonely landslide” at all. Democrats netted two seats, defeating Republican incumbents in New York, Maryland, and New Mexico, while appointed senator Pierre Salinger lost in California. But this outcome came after the election cycle of 1958—the best performance for either party in any Senate cycle in the postwar era. Including the subsequent results from the new seats from Alaska and Hawai’i, a 49-47 Senate was transformed into a 65-35 one.

As always occurs with wave elections, fairly weak incumbents won in tough states (Indiana, Wyoming) or as a result of flukes (Utah, when a conservative independent siphoned votes away from incumbent Arthur Watkins; California, after the GOP senator and governor disastrously tried to switch jobs; and Ohio, where Stephen Young’s upset win was almost entirely attributable to unions turning out voters to block a right-to-work referendum). In a neutral environment, it seemed unlikely that most of these seats would be held.

Democrats had additional vulnerabilities in 1964. In North Dakota in 1960, Quentin Burdick had won a special election by campaigning against Dwight Eisenhower’s farm policies (“Beat [Ezra Taft] Benson with Burdick”); he would first stand for a full term in the heavily Republican state in 1964 having to defend the policies of a Democratic agriculture secretary. Deaths of Democratic senators in Oklahoma and Tennessee produced internal party tensions; in both cases, a contested primary led to the ouster of the appointed senator and his replacement by a weaker, more liberal nominee.

Republicans, on the other hand, had only nine seats to defend. In every state but Arizona, where Barry Goldwater vacated his seat to run for President, they had an incumbent who had survived the disastrous environment of 1958.

Class of 1958 Democrats recognized their vulnerability, and their need to stay on LBJ’s good side. One of my favorite LBJ calls came with Indiana Democrat Vance Hartke, after the near-collapse of the tax bill in the Senate Finance Committee, as logrolling amendments by committee members exploded the cost of the bill. Getting the bill passed—and the political benefits it would produced—required some blunt lobbying of Hartke, who wanted a tax break for a musical instruments plant in Elkhart, Indiana. ...