Art credit: David Clark

January 20 will be a banner day for the Republican party. On the steps of the Capitol, Donald Trump will be sworn in as the nation’s 45th president. In the building behind the ceremony, his party will be ready to enact his program with a sturdy congressional majority. The GOP is in historically strong shape in state capitols across the nation, set to implement conservative policy reforms from Idaho to Florida and just about everywhere in between.
But if the Republican party were a publicly traded company, January 20 would be the day to sell, sell, sell. This may sound counterintuitive, but the verdict of history is clear, if not quite unanimous: The moment a party achieves total control of the government is the moment just before power begins to slip through its fingers.
Usually, the downturn begins quickly. First the marginal members of the congressional coalition begin to waver in their loyalty, then the midterm revivifies a seemingly moribund opposition. While the incumbent party usually wins its first reelection bid for the White House (Jimmy Carter being the only exception in the last 125 years), the other side retains a substantial footprint in the government. Their numbers are usually strengthened in the second midterm—at which point they often gain control over Congress.

There are exceptions, of course. The Great Depression during Herbert Hoover's administration brought pain beyond compare, yet the economy turned a corner about the time Franklin Roosevelt was inaugurated. That, combined with his vigorous domestic agenda, helped him expand his political coalition in his first term. John F. Kennedy took office near the beginning of a fantastic economic boom. That, combined with his untimely death in 1963, boosted the Democrats' fortunes under Lyndon Johnson, at least for a time.
Even so, it has been the dominant pattern in American politics for almost 200 years. Parties are much more successful at acquiring political power than they are at keeping it. The reason for this is simple: Ours is a very hard country to govern.
Parties face three challenges that eventually prove insuperable. First, America is an extremely diverse nation, yet we have but two major political parties. Party coalitions are quite heterogeneous, and it is difficult to keep so many far-flung factions within the coalition happy at all times. This is especially the case when the opposition is constantly endeavoring to poach marginal supporters. Because the difference between victory and defeat is rarely larger than 10 points, it does not take a lot of work to swing just enough voters.
Second, our system makes parties look like governing failures. The Constitution carefully distributes governing authority across multiple institutions—the presidency, two chambers of Congress, the courts, state governments. It is hard to induce these disparate entities to coordinate their efforts to deliver on the bold promises candidates make on the stump. This is a feature, not a bug, of our system, which typically requires a broad and durable consensus before big changes can be made. Candidates rarely endeavor to manage expectations when they're electioneering—and that leaves the victors on the hook when the government does not deliver what they promised on the stump. And, of course, the opposition is always eager to tell voters that only they can make the government work.
Third, exogenous shocks to our polity are common. Wars, recessions, scandals, domestic crime waves, messy foreign entanglements—history is replete with instances when events such as these totally altered the political playing field. Sometimes, events strengthen a party's governing hand, as was the case with JFK's assassination and the 9/11 attacks. But more often than not, voters blame the party in charge for the new problem. The most frequent culprit is the business cycle. Ruling parties get the blame for recessions, which tend to recur every 5 to 10 years.

Some politicians are better able to ride the tides of fortune than others. Franklin Roosevelt, for instance, was a master at holding the Democratic party together; on the other hand, Jimmy Carter, who like FDR was elected with an overwhelming party majority, proved himself incompetent at the task. Still, the tide always crashes into the shore eventually. For all his acumen, Roosevelt found his governing coalition torn asunder in 1938. Even though the party retained a congressional majority until 1946, the liberals in Congress were overwhelmed by a bipartisan conservative coalition, which retained power until the 1964 election.
So Republicans would do well to make hay while the sun shines, for sooner or later it is going to set. Ironically, nobody furnishes a better example of how to make use of a fleeting majority than Barack Obama and congressional Democrats. Blessed with a supermajority during 2009-2010, they implemented many sweeping policy changes with impressive alacrity—as if they knew that the moment would soon pass. Indeed, it did. This one will, too. Republicans should make the most of it while it lasts.
Jay Cost is a senior writer at The Weekly Standard.