"Why should views on (for example) gay marriage, taxation, and U.S. policy toward Iran have much of anything to do with one another," Silver asks "the answer is that it suits the Democratic Party and Republican Party's mutual best interest to articulate clear and opposing positions on these issues and to present their platforms as being intellectually coherent."
In his excellent book Political Ideologies and Political Parties in America, Georgetown University political scientist Hans Noel argues that the causation goes in the other direction. In the old days, political party professionals hated ideologues because ideologues undermined the parties' best efforts to form winning electoral coalitions and disperse the spoils of power. What happened was that ideologues constructed ideologies — first the Progressive movement evolving into modern liberalism, and then ideological conservatism arising in the 1940s and 1950s to counter it — and the ideologies captured the parties.
Whether you see this Silver's way or Noel's, an interesting question is whether these ideologies are really arbitrary.
One big piece of evidence that they are not arbitrary, I think, is that you see similar ideological bundles around the world. The specific issues debated in Canada are different from those in the United States, and the policy status quo is quite different — implementing something like Obamacare would be a deeply right-wing move in the Canadian context. Still, you see a Conservative Party that is more nationalist, more business-friendly, more anti-abortion, etc.
By the same token, over in India they have a Hindu nationalist party that is also pro-business, and a pluralistic party that is more invested in redistribution. In Germany, there is a niche political party dedicated to environmental issues and pacifism and you will be shocked to learn that it typically seeks to form coalitions with the party rooted in the trade union movement.
In Spain, it was the Workers Party that brought marriage equality into law and in France it was the Socialist Party.
In other words, all around the world you tend to see a similar basic pattern. Support for progressive taxes "goes with" support for ethnic and other minority group concerns and environmentalism, while the pro-business party is usually also nationalistic and supportive of traditional religious values. This is true even in countries with well-entrenched multi-party systems.
To be sure, not every country follows this pattern. But what's notably is that the countries that defy the pattern tend to simply not have well-defined ideological parties.
In Japan, for example, the Liberal Democratic Party is a big tent catchall primarily organized around winning elections and distributing pork. Policy fights happen between LDP factions and not as a consequence of party competition. The opposition Democratic Party of Japan is largely defined by its opposition to the LDP, rather than by specific ideological stances. The two main Irish political parties, Fianna Fail and Fine Gael, trace their origins back to the split within Sinn Fein over the Anglo-Irish Treaty. People don't argue about the Treaty now but it was a huge deal in the 1920s, 1930s, and 1940s and people ended up inheriting party allegiances. But traditionally both parties have been more or less "conservative" in the traditional sense.
What you don't see around the world is a party system where the ideologies are flipped. Where the hawkish party supports religious traditionalism and a more expansive welfare state, while facing opposition from a dovish socially progressive pro-business party.
This makes me think that the basic left-right ideological alignment may reflect some objective property of reality and not just the contingent paths of history. Maybe it's "really true" that these two ideological bundles are more coherent than the alternatives. Or maybe it's in the structure of interest group politics. Women are poorer than men, so maybe it's natural for redistribution to bundle with feminism and anti-redistribution to bundle with patriarchy.
In case you were hoping for actual political news rather than a long digression about comparative politics, it turns out Hillary Clinton is running for president. You can see all of Vox's Clinton coverage or just check out my two pieces on her tenure as a senator and her vote to authorize the invasion of Iraq.
Le Tigre, F.Y.R.