ST. GEORGE, W.Va. -- Up several thousand feet in the Pheasant Mountain area of West Virginia, the course of American politics suddenly becomes clear.

Lace up your hiking boots, follow Smoky Hollow Road for two miles, take a left, pull into a grassed-over parking lot and head up the Clover Trail, then climb into the thickness of the Monongahela National Forest. This is like no mountain trail you have ever traversed; it follows an old logging railroad through five switchbacks that nearly a century ago the D.D. Brown Lumber Co. used to haul lumber. The train would inch one way and then switch back -- thus the term -- to cross the mountain by going backward on the next switchback.

It is those switchbacks amid the hemlock and yellow poplar that sent lumber from the Clover Run Valley to the unincorporated village of Moore on its way to market in Philadelphia and Pittsburgh. And it is those switchbacks that illustrate the course of American politics, for in the past 150 years the presidency and the Congress have consistently switched from the control of one party to another, and then switched back.

Indeed, there is no more vivid example than West Virginia itself, which in November will fall in Donald J. Trump's column but which a generation ago was devoutly Democratic. It was here, in 1960, that Sen. John F. Kennedy of Massachusetts defeated Sen. Hubert H. Humphrey of Minnesota in one of the classic presidential primaries. Later that year, Kennedy took 52% of the vote against Richard M. Nixon, and the state's eight electoral votes went into the Democratic column.

Some 28 years later, another Massachusetts Democrat, Gov. Michael S. Dukakis, captured the same 52 percentage points, though by that time the Mountaineer State possessed only five electoral votes. By 2012, yet another Massachusetts governor was running for the White House, and this time the Republican, Mitt Romney, prevailed with 62%. That is a massive change -- a massive switchback, to apply the metaphor -- in only 24 years. Battered by the party's positions on gun control and coal, the Democrats went from a slender majority to a decisive minority of about a third of the vote. And in 2016, Trump took West Virginia with 68 percentage points.

Switchbacks appear everywhere across the American political landscape.

Political professionals consider the Philadelphia suburbs a vital key to the 2020 race, and this switchback works to the Democrats' advantage in a state they believe they must win if former Vice President Joseph R. Biden Jr. is to capture the White House.

In the 1988 election, Vice President George H.W. Bush took the four suburban counties around Pennsylvania's biggest city by the landslide margin of 61 percentage points. Four years ago, Trump captured only 41% of the vote there. In Delaware County, a suburb abutting the city of Philadelphia that has been reliably Republican since the Civil War, the switchback is particularly vivid; less than a year ago, Democrats swept all five seats in the county council. They also won county-council majorities in nearby Bucks and Chester counties.

Think again about West Virginia's Clover Trail. There the path ahead seems unclear. The trail often is obscured. And on the slopes of the mountain, the old timbers have been felled.

The same is true in our politics. Today no one knows for sure whether Trump will win a second term, and whether the Trump ethos will endure in the Republican Party after he departs. Also, no one knows for sure whether Biden would govern as a centrist, which is his inclination, or would lean left, as many of his reluctant supporters are pushing him to do -- a prospect Trump sought to use to his advantage in the Republican National Convention when he said, "The radical left will demand he appoint super-radical-left wild crazy justices going into the Supreme Court."

All around, the old timbers of American politics are down: Rep. Eliot Engel of New York, the powerful 16-term incumbent who was chairman of the House Foreign Affairs Committee, was defeated this summer in a Democratic primary. Reps. Joseph Crowley, also of New York, the fourth-ranking House Democrat, and Michael Capuano of Massachusetts, a traditional Bay State Democrat, were felled in 2018. And establishment Republicans have fallen from grace in the Trump years. Neither Romney, the party's 2012 nominee, nor former President George W. Bush, who won GOP nominations in 2000 and 2004, spoke at the Republican conclave. All the living Democratic presidential nominees except Dukakis and former Vice President Albert Gore Jr. spoke at the party's virtual convention earlier this month.

It turns out that switchbacks are the way of American politics. The Republicans won the first three presidential elections of the last century, and then the Democrats won the next two. The Republicans took three consecutive elections beginning with 1920, the Democrats five straight after that. The pattern has basically continued until our own time. We go one way for a while, then we go the other way.

The only question is the length of each period of control. Between Richard M. Nixon (1969) and George H.W. Bush (president until 1993), the Democrats controlled the White House for only four years. That's an aberration, but then again, that Democratic president, Jimmy Carter, was something of an aberration -- but one who highlighted another transition in our politics.

On Election Night 1976, when the former Georgia governor prevailed, it seemed possible that the Democrats -- winners of every state of the Old Confederacy but Virginia -- might reclaim their birthright of the Solid South, which Nixon had pierced in 1968. It was not to be. Four years later, former Gov. Ronald Reagan of California swept the South except for Carter's Georgia home. The elder Bush took them all in 1988.

Another tradition of American politics is the post-election postmortem. In 2012, the Republicans were in despair over their poor performance among women and minorities and vowed to do better. Trump's triumph postponed that reckoning. Even if the Democrats win this year, they will undertake some soul-searching. "There will be tension," said Sen. Edward J. Markey of Massachusetts, "but it will be good tension." Markey faces a tough primary Tuesday against Rep. Joseph P. Kennedy III, a generational rival who thinks he sees a switchback. And so it continues.

North Shore native and Pulitzer Prize winner David M. Shribman is the former executive editor of the Pittsburgh Post-Gazette.

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