For most Americans, presidential elections are the key events in our politics. Journalists and academics often obsess about the implications of presidential races and endlessly discuss the possibility of a “critical election” that will realign our politics for generations to come. At best, midterm elections are seen as limited corrections to the course set by important presidential elections.

Ordinary voters seem to share this view of midterms as less important sideshows to the main events. As a result, voter turnout in midterm elections is one-quarter to one-third lower than in presidential elections.

But many midterm elections have been at least as important as the majority of our presidential elections, if not more important. In some cases, they have resulted in seminal legislation that reshaped America, and in other cases, they signaled transformations of our political parties, our governing institutions and American politics in ways that would drive political debate for decades. Indeed, what happens this year may be just as important as President Trump’s stunning rise in 2016 and whatever happens in 2020.

In 1995, political scientist David Mayhew (full disclosure, he was my adviser in graduate school) identified what he described as “innovative” midterm elections. These elections elevated a new dominant congressional coalition that went on to have considerable success implementing a fresh agenda and remaining in power.

Mayhew identified four midterms that met these criteria:

1810, when the Jeffersonian Republican “War Hawks” who enacted a nationalist economic agenda gained power, setting the stage for the War of 1812.

1866, when, responding to white Southern intransigence after the Civil War, Radical Republicans swept to power and implemented far-reaching and egalitarian Reconstruction policies. ...