Why power in Congress is now so precarious

Control of Congress has become so precariously balanced between the two parties that it may now be subject to the butterfly effect.

The butterfly effect is a mathematical concept, often applied to weather forecasting, that posits even seemingly tiny changes – like a butterfly flapping its wings – can trigger a chain of events that produces huge impacts.

Because it has become so difficult for either party to amass anything other than very narrow majorities in the House and Senate, the exercise of power in both chambers now appears equally vulnerable to seemingly miniscule shifts in the political landscape.

Just in the past few weeks, a revolt by a small band of House conservatives effectively denied the Republican majority control of the floor for days. At the same time, a Supreme Court voting rights decision that might affect only a handful of House seats has raised Democratic hopes of recapturing the chamber in 2024. In the Senate, the extended absence of a single senator to illness – California Democrat Dianne Feinstein – prompted an eruption of concern among party activists over the upper chamber’s ability to confirm President Joe Biden’s judicial nominations.

In different ways, these developments are all manifestations of the same underlying dynamic: the inability of either side to establish large or lasting congressional majorities.

Viewed over the long-term, majorities in the House and Senate for the past 30 years have consistently been smaller than they were when Democrats dominated both institutions in the long shadow of the New Deal from the 1930s into the 1980s. And those majorities have grown especially tight since former President Donald Trump emerged as the polarizing focal point – pro and con –of American politics.

Since the Civil War, only rarely has either chamber been as closely divided between the parties as it is…