We live in very partisan times; everyone knows this.
But few things demonstrate the degree of that partisanship like the two charts below, which come courtesy of the blogger (and contributor to the liberal blog Daily Kos) Xenocrypt.
Both charts compare how each congressional district voted for president in two successive elections. The first compares how they voted for President Obama in 2008 and 2012, while the second compares how they voted for two-time Democratic candidate (and two-time loser) Adlai Stevenson in 1952 and 1956.
As you can see, the votes in 2008 and 2012 for Obama fall on an extremely straight line, suggesting little variation between the two elections. In addition, basically all of the districts held by Democrats (these are the blue plots) predictably favored Obama, while almost all the Republican-held districts (red) favored the GOP candidates.
Look back 60 years, though, and there is significantly less order to this chart -- even though both the 1952 and 1956 elections featured exactly the same matchup between Stevenson and President Dwight Eisenhower.
Even as the matchup was the same, though, the results district-by-district varied widely between the two elections.
You'll also notice on this chart that there are many more Democratic-held districts that voted for the Republican Eisenhower (more blue plots in the bottom-left quadrant).
The reality is that Americans are so partisan and races are so nationalized that it's pretty unlikely we'll see more elections like the ones in 1952 and 1956.
For better or worse, the presidential vote in any one congressional district is eminently predictable, and the vote for that district's representative in Congress will be heavily correlated to that predictable outcome in the presidential race.