New Year’s Day is a good time to take a long look backward with a cautious eye toward possible futures. My guide here is RealClearPolitics analyst Sean Trende’s 2012 book “The Lost Majority,” whose bold thesis was unduly neglected by political scientists spinning tales of a permanent New Deal Democratic majority.

Trende’s thesis instead was that Democrats’ big 1930s majorities were not enduring. Their 1940s presidential victories owed more to Franklin Roosevelt’s wartimes and Harry Truman’s Cold War leadership than to big-government domestic policies, which no Congress elected between 1938 and 1958 supported.

Instead, the real majority-former from 1950 to 1990 was Dwight Eisenhower. He won twice, as did his vice president, Richard Nixon. Ronald Reagan, whom Eisenhower admired and regarded as a suitable future president, according to amateur historian Gene Kopelson, in the 1980s carried even more states than Eisenhower had in the 1950s.

Eisenhower, who owed his national prominence to Roosevelt, regarded attacks on New Deal programs as imprudent despite the skepticism of big government he expressed after leaving office. Reagan, a four-time Roosevelt voter, coming to office when big government was popular, could oppose its expansion but not its elimination.

Seemingly permanent Republican control of one branch of government and Democratic control of another often led to constructive compromises. The parties’ divergent historical heritages — Democrats split between Southern segregationists and labor union militants, and Republicans between small-government localists and big-government internationalists — allowed deft politicians of both parties to fashion careers even on unlikely turf.

In “The Lost Majority,” Trende argues that Bill Clinton brought in a new partisan balance in the 1990s. Starting in that decade, old party loyalties started to fade, and long-established patterns of ticket-splitting were replaced by straight-ticket voting. Hitherto little-known politicians in their 40s upended four-decade political tradition.

Clinton ended the apparent Republican lock on the presidency in 1992, and Newt Gingrich ended the Democratic lock on Congress in 1994. College graduates, starting in 1996, moved toward voting Democratic, while white Southerners trended Republican.

In states and cities, starting with Republicans Tommy Thompson in Wisconsin and Rudy Giuliani in New York, followed by other Republicans and some Democrats, including Clinton, leaders cut welfare dependency and violent crime by more than half.

That removed problems that had helped Republicans in the suburbs (the worst thing a politician can do electorally is to solve the problem he campaigned on). Meanwhile, Republican efforts to make inroads among Black and Hispanic people by not opposing racial quotas and heavy immigration produced only small countervailing gains.