This is diagram shown in Mr. Krugman´s post.
Essentially this is a version of the Nolan diagram, which David Nolan suggested in 1970, here is a version, which turns the original graph by 45° (for ease of reference and comparison with the above), from here.
Here is another version, visualized with examples, also turned by 45° by myself from here, which seems to confirm that even among politicians the upper right area is thinly populated..
Now I don´t have data for US voter preferences, but found the following for Swiss party preferences. Interestingly here four out of the seven larger parties are in the upper right quadrant.
Large dot: country average, single dot: individual canton
The parties in the various quadrants (major parties in bold including last voting shares:
- Upper left box / "Liberals" in Mr. Krugman´s diagram: Social Democrats (SP, 20%), Greens (Grüne, 7%), Communists (Partei der Arbeit), Evangelical People´s Party (EVP); note: EVP is probably rightly classified as centrist party
- Upper right box / "Liberterian" in Mr. Krugman´s diagram: Green Liberals (GLP, 7%), Christian Democrats (CVP, 11%), Conservative Democrats (BDP, 5%) and Liberals (FDP, 16%), note: both Green Liberals and Liberals are classical liberals
- Lower right box / "Conservatives" in Mr. Krugman´s diagram: Swiss Peoples Party (SVP, 25%), Democratic Union (EDU), Ticino Leage (Lega)
- Lower left box / "Hardhats" in Mr. Krugma´s diagram: Swiss Democats (Schweizer Demokraten), note: far right party not represented in national parlament