Why are politicians polarized?

My understanding of the political science research on this topic was that political polarization post-Internet was mostly a USA-specific thing, and you did not see as strong a polarization elsewhere when you take a systematic look.

(It wouldn't be surprising if people base their impressions "politics is so polarized these days" solely on the one example of the USA and are badly wrong about their generalization, because due to media and the Internet especially, everyone pays a ton of attention to American politics, whether or not they want to, and typically ignore other countries. For example, Japanese politics - out of the ~200 countries worldwide, Japan is one of the most important countries, a member of G8, fourth-largest economy etc - but can you name the current PM - not the ex-PM who was assassinated 2 weeks ago, assuming you remember that at all, but the current PM? I doubt it. I thought I did but then I checked and I was remembering the previous one, Suga. Now, can you tell me if Japanese politics is more or less 'polarized' in 2022 than it was in 2012? Personally, I don't have a clue.)

So, since it's US-specific and changes over time, most of these hypotheses aren't even wrong because they are explaining observations which don't exist. In countries with extensive public funding for campaigns, how can changes in 'donating' happen, much less drive the polarization which also didn't happen? (Not that money matters remotely as much as people think in the first place, and is mostly a reverse causality deal: victors raise money, money doesn't raise victors. Ask Bloomberg how easy it is to buy a vote.) And they also don't explain why it would increase when they are levels: politicians have always been irrational, why would they be moreso now? That's what would then need to be explained, otherwise it's just passing the buck.

This is decidedly not what we see in the US (or in any country) - the two parties’ views differ substantially.

The views of the parties differ substantially on some issues but not on others. It's quite natural that most of the focus of the public debate is on differences and not on what's the same.

A recent post [LW · GW]on LessWrong wrote:

Certain studies emphasize partisan differences, but most find that the ideology of governing parties has indiscernible to small influence on policy, one meta-analysis establishing that the ‘average correlation between the party composition of government and policy outputs is not significantly different from zero’.

George Bush campaigned on "No national building" and went to start the wars in Afghanistan and Iraq which were massive nation-building projects. 

I upvoted this post - it is a good stab based on the easily accessible public information and a look at relevant theory.

Hypothesis 5 is the path to victory here. The core problem is that (almost) everyone is wrong about (almost) everything, and the least wrong people do not form a group. Some examples:

Moderates do not exist. By this I mean there is not and never was any such group of people. The existence of moderates is a mistake in tabulating the results of political surveys. The mistake looks like this: you might have a survey with multiple responses, and one person responds:

Q1. How do you feel about gay marriage?
A1. Gay people should have civil unions rather than marriage

Q2. How involved should the government be in the economy?
A2. Government should keep taxes low

But another person responds with:

Q1. How do you feel about gay marriage?
A1. Gay people should not be allowed to get married, or adopt, or teach children

Q2. How involved should the government be in the economy?
A2. Government should heavily tax the rich and important industries should be nationalized

Since both answers for the first person were conservative, the surveys marked that person as "very conservative." The second person, with one extremely conservative answer and one extremely liberal answer, got marked as a moderate. It turns out if you graph the policy preferences of people who are moderate, undecided, or independent, they land all over the ideological map.

But most politicians, pundits, campaign staffers, and voters believe in moderates.

Money does not win elections. The narrative is straightforward here: the side with the most money usually wins, so money most be what caused victory. The best natural experiments for this are repeated contests between the same two people, and when we look at these contests we find that the effects of money are very weak: the number I remember is doubling the money brought 1% more of the vote and halving it cost 1%.

The alternative explanation based on this is the more likable/popular candidate receives more political donations.  This one passes the smell test: if we invert these stories, it would be very weird if the actually-more-popular candidate systematically got less money, and it would be wild if the person who got more money systematically lost the election.

But most politicians, pundits, campaign staffers, and voters believe money wins elections.

Americans are not politically engaged. This one is something that campaign people understand, but the other groups mostly ignore in practice: a huge chunk eligible voters don't vote. Campaigns target the populations that do vote, and policy is heavily influence by what is popular in campaigns.

The key insight here is that both parties in the US tend to enforce this rather than try to expand the electorate. While the blue team is notionally friendlier to this idea than the red team, what they do in practice is try to increase the participation rate of groups which they already expect to support them. This is why voter turnout is the conversation: the default election strategy is to identify the groups of likely voters and that are likely to support your side, then try to get the number of them that show up on election day as close to 100% as possible. At the same time, it is common to try and reduce voter turnout for the opponent. This is the mechanism of negative advertising - it drives people to stay home and not vote at all.

But most politicians, pundits, and voters believe campaigns are trying to persuade the public to vote for them instead of the other person. This is similar to the mechanism of the primaries hypothesis above, but primaries are explicit to party membership and activity.

Some issues are more relevant than others. The word political scientists use for this is salience. In elections, no candidate is ever evaluated by the public on the basis of all of their positions; instead, there are usually a few issues the election becomes "about", and the candidates which are better positioned on those issues tend to win (subject to the turnout considerations above). This one also passes the smell test - even the smallest elections encompass a wide range of issues, and I definitely expect attention bandwidth to be a limiting factor.

This is why messaging is so important - if a side can keep messaging discipline, then what the message is about is more likely to be what the election is about. I think this is also what drives a lot of those "X is really about Y" style arguments - these look to me like bids to increase the salience of one issue at the expense of another.

But, most politicians, pundits, and campaign staffers tend to act like the stuff they care about should be the issues of the campaign. This is much like your echo chamber hypothesis above.

All of this is compounded by all the usual problems like how difficult social research is, statistical incompetence, professional biases, etc.

In summary, I feel like the true model is a model of everyone else's models being borked.

Not sure this is a good use of the MVT but I came to the view long ago that MTV is a really bad model for general voting and elections but is a good model for party formation and platform - and I suppose, therefore, primary voting. I think as you start collapsing the complex issue space into a common dimension as it typically illustrated one should expect to see a multi-modal distribution. The modal centers then become the party platform locus.

Alternate theory:  virtue signaling over policy preference.  Voters mostly don't care about the details, only about showing their family and peers that they're part of the tribe, and have the "correct" passion about politics.

This leads to one-upsmanship of extreme ideas, and acceptance that supporting this is the way to belong.  This is how voters get polarized.  And this style of polarization means they hate moderates (because they weaken the tribe), so politicians don't succeed unless they are at least as polar as their base. 

The obvious thing to keep in mind is that people dislike 'inauthentic' politicians but there are many things the people want in politicians. If a politician wants to portray a certain image to match what people like, they have to pick the policy positions that go along with it to avoid said label. Said images are not so evenly or finely distributed as policy positions, so that tends to lead to significant differences along these axes.

Then, over time, the parties accrete their own new images too, and people have to position themselves in relation to those too...

Interesting topic! My political science capstone course covered some of these questions, so I ended up writing about/researching these concerns pretty frequently. Basically, the main explanation points out that recent politicians have been campaigning on moral grounds at increasingly alarming rates. They frame their opponents as not only less informed/less fit to hold office than themselves, but portray rivals as legitimate dangers to the country. By assigning positive moral value to their own platforms and negative moral value to the ideas of their opponents, they intensify polarization by convincing voters that compromises/middle ground positions are unthinkable. If a member of the opposing party isn't merely someone with a differing opinion about immigration, for example, but a representation of a perverted philosophy, it follows that voters wouldn't want to elect politicians that are open to collaborating with them or engaging in meaningful conversation with them. Moderate candidates are consequently viewed as unreliable figures that compromise their beliefs.

Unfortunately, this attitude affects local and state level politicians as well as voters. Politicians well outside the D.C. sphere pledge their support for Trump, for example, to align themselves with a broader ideological movement. In turn, Republicans that might not agree with Trump's unprecedented behavior feel pressured to include pro-Trump messages in their advertisements and speeches in order to secure votes (regardless of whether they actually approve of Trump's actions). This prominent type of polarization results in more extreme ideological differences than we've seen in earlier decades.

Sadly, this wave of polarization also lends itself to the two major parties essentially operating in different realities. We've observed politicians promote bizarre conspiracies (MTG) and openly distrust reliable information because it's presented by members of an opposing faction. Furthermore, the religious element present in many campaigns (especially those of Republicans) presents an additional challenge as candidates aligned with faith-based beliefs often receive a semblance of immunity from their bases.

I'm basically a "moderate," I don't like tax cuts for the rich and am angry about Dobbs. But I won't be voting for a group of people who gleefully advocate firing me from my job because I don't support transgenderism and MeToo. I'll probably sit out the midterm elections

I think it's wishful thinking. People respond better to "I'll give you 100% of what you want" than "I'll give you 66% of what you want." Joe Manchin isn't in the echo chamber and has proven he can win a state Democrats normally write off. But there's far more support for "kick Joe Manchin out of the party" than "make Joe Manchin our standard-bearer." 

I think when you look at level remaining support for truly disastrously unpopular governments, it seems about 50-60% of population view politics as tribal and would vote for their tribe no matter who the candidate is or what the policy statement. Furthermore, voters are likely to vote for party rather than candidate because you only get your preferred policies if you your party wins. Of the remainder, a substantial proportion are still tribal and would only vote for the opposition rarely in cases where fed up. ("death of a thousand cuts"). Truly swinging voters probably have a disproportionate influence on elections. As an outsider looking in on USA, it seems to me that polarization is being driven by a balkanized media (people can effectively choose a "reality" from their news sources). These can fan tribalism (it is in the media interest) using the traditional tribal identities of race, religion and class. Excessive power given to president compared to congress bypasses the ameliorating influences that parliamentary systems possess. The voting system in USA also makes it extremely hard for other parties to attract any votes so the art of compromise necessary in proportional systems is missing (and indeed despised).

When looking at polarization in the US, it's more at the Congressional level than at the presidential level and this is often due non-competitive general elections so the winner of the primary will be the winner of the general election. This has gotten worse as gerrymandering has continued to increase. In more competitive races, you see the political parties trying to select more moderate candidates. 

[party elites, politicians and donors] have much more radical views than the median voter of their party

This is quite false. The median conservative wants gay marriage made illegal, abortion banned, significantly lower taxes, and does not care about human production of CO2. The median liberal wants men competing in women's sports, at-will abortion up until birth, wealth re-distribution, and global reductions in CO2 emissions. Yet these views are reflected in few of either party's senators and congressmen. I wouldn't take Yglesias's word on how radical politicians are given most all of what he writes is democratic propaganda.