Great article over at the Economist about how the US Constitution, our first-past-the-post voting system, and demographic changes give Republicans a significant advantage in legislative elections.
The source of this discrepancy is that Democrats will win their seats with big majorities in fewer districts, whereas Republicans will prevail by narrower margins in a larger number of districts. In 2016 Democrats who beat Republican opponents won an average of 67.4% of the two-party vote in their districts, whereas Republicans who defeated Democrats received an average of 63.8%. This imbalance is partly due to deliberate attempts to create districts that provide such results, and partly just down to the fact that Democrats tend to live more tightly bunched together in cities. Together, these two factors put up quite an obstacle. According to our model, the Democrats need to win 53.5% of all votes cast for the two major parties just to have a 50/50 chance of winning a majority in the House.
If this imbalance were limited to a single chamber of the legislature, or a single election cycle, the Democrats’ frequent carping about a stacked electoral deck might sound like sour grapes. All electoral systems have their oddities. But changes in where Americans live and contradictions in their constitution — a document designed to work with many weak factions that has instead encouraged and entrenched an increasingly polarised two-party system — have opened gaps between what the voters choose and the representation they get in every arm of the federal government. In recent decades these disparities have consistently favoured the Republicans, and there is no reason to think that trend is going to change on its own.
In the past three House elections, Republicans’ share of House seats has been 4-5 percentage points greater than their share of the two-party vote. In 2012 they won a comfortable 54% of the chamber despite receiving fewer votes than their Democratic opponents; in 2014 they converted a 51% two-party-vote share into 55% of the seats.
Such comparisons are harder for the Senate, where only a third of the 100 seats are contested in any election. But adding together all the votes from the most recent election of each senator, Republicans got only 46% of them, and they hold 51 of the seats.
Then there are presidential elections:
In all the world’s other 58 fully presidential democracies — those in which the president is both head of state and head of government — the winning candidate gets the most votes in the final, or only, round of voting. But due to the “electoral college” system that America’s founders jury-rigged in part to square the needs of democracy with the demography of slavery, this does not hold true for America. States vote in the college in proportion to their combined representation in both houses of Congress. This set-up means that a candidate who wins narrowly in many small and smallish states can beat one who gets more votes overall, but racks most of them up in big majorities in a few big states.
During almost all of the 20th century this did not matter much; the candidate who got the most votes won every election from 1896 to 1996. But both of the past two Republicans to win the presidency have received fewer votes when first elected than their Democratic opponents did. In the contest between Al Gore and George W. Bush in 2000, this margin was a modest 0.5 percentage points. In 2016, however, it was substantial: Hillary Clinton’s lead of 2.1 percentage points was larger than those enjoyed by the victorious John F. Kennedy in 1960, Richard Nixon in 1968 and Jimmy Carter in 1976.