Congress did not become a national punchline for any one specific reason, and thus its failures cannot be too broadly summarized. The institution is broken in ways apparent and ambiguous, from the capacity of the individuals charged with making the laws to the malfunctioning processes by which they are made. That said, there can be no understanding Congress’s existential plight without recognizing, at a foundational level, a basic structural problem: There are 435 districts represented with a vote in the House of Representatives—and only a few dozen of them are contested in November.

Even in a “wave” cycle like 2018, when Democrats flipped 43 GOP-held seats in a climate that was conducive to mass mobilization and unpredictable results, nine out of ten House seats remained locked down by one occupying party or the other. Despite a pair of historically disruptive midterm election cycles in the past decade (Republicans flipped 63 Democratic-held seats in 2010), the percentage of true swing districts is smaller than at any point in American history. When the overwhelming majority of lawmakers know the renewal of their job is decided not by a high-turnout, ideologically diverse November electorate but by a low-turnout, ideologically homogenous primary electorate, you have a germ of dysfunction so contagious that it can systematically cripple an entire system.

Which is precisely what is happening to Congress. Recognizing how this consolidation of power has bifurcated the voting public and reduced practically every debate to zero-sum tribal warfare, most elected officials—whether hailing from districts that are deep red or dark blue—operate according to the reality that their career is endangered primarily, if not exclusively, by extreme elements within their own party’s base. Bipartisan collaboration, no matter how worthwhile, is instinctively discouraged; partisan brinksmanship, no matter how counterproductive, is encouraged and recompensed. Telling voters what they want to hear, even if untrue or unrealistic or both, is the recipe for reelection; telling voters what they need to hear, especially when it is aggravating or inconvenient, is a ticket to the unemployment line.