Are American politics approaching a new era?

There is a tide in the affairs of America, and the big question is whether right now the political seas are at ebb tide or flood tide.

American politics is guided by these tides, and in retrospect, their movements become clear. Future students of history may come to see that contemporary America was shaped by two of them, each about four decades long. Their precise beginnings and ends are murky, but the general shape of them — the swells and the troughs — may be apparent when mid-21st-century historians begin to examine what we now regard as lived experience and modern history. For them, all this may seem like ancient history.

The first of these tides might be said to have started in 1932 and almost certainly will come to be seen as a great Democratic era, populated by giants (Franklin Delano Roosevelt, Harry Truman, John F. Kennedy, Lyndon B. Johnson) and marked by the conquest of both the Great Depression and the Second World War; a great expansion in the role of government; and soaring rhetoric about ending injustice and smoothing out the rough edges of life.

The second tide might be thought of having begun in 1976 and may be seen as a dominant Republican era, populated by a powerful mixture of establishment figures (Richard M. Nixon and George H.W. Bush) and rebels (Ronald Reagan and Donald Trump), and marked by the conquest of Soviet-style Communism; by a fundamental rethinking of the role of government in everyday life and in the economy; and by a celebration of the philosophy and arts of entrepreneurship.

What ties them together — what ties together almost a century of American life — is the conviction, held dearly by political figures in both parties, that politics is the expression of upswells of public will. Even though the rhetoric in both waves focused on the middle class — its growth and shrinkage, its prospects and perils — both tides realized their power through the welfare, interests and inclinations of blue-collar Americans. The animating conviction was, as Mr. Kennedy might put it, that a rising tide — whether because of the new opportunities that accompanied new rights or the liberation that came from the removal of government interference in the economy — lifts all boats.

And so the shifting loyalties of what we might call “working America” — not middle-class Americans nor soccer moms in the suburbs, important as they have been in stump speeches — are the moving parts of the country's politics.

That was true in the 19th century, as the elections of Andrew Jackson (1828 and 1832) and William Henry Harrison (1840) displayed. It began to coalesce in modern times with the unsuccessful 1928 campaign of Democratic Gov. Al Smith of New York and was consolidated with the election of FDR in 1932.

Under Mr. Roosevelt and the Democrats who followed the New Deal with the Fair Deal (Mr. Truman), the New Frontier (Mr. Kennedy), the Great Society (Mr. Johnson) and the New Covenant (Bill Clinton), rights were expanded and horizons were broadened.

The first two years of the Nixon presidency can almost be regarded as an extension of the Democratic wave, with the creation of the Environmental Protection Agency and with the administration winning passage of a landmark income-floor plan in the House but failing to win support in the Senate. It was the Nixon team's pillorying of a similar 1972 plan forwarded by Sen. George Mcgovern — a flip from Nixon approval of the plan to opposition to it — that began the transformation from one era