This is a very good point.

I take some of those points. I don't know the state or trend of polarization in other countries (only countries with two main parties would be of interest for this model, multi-party elections yield a different system). Though I maintain that one country is still an observation to be explained, requiring a hypothesis. I could also believe that donations or activism don't drive election performance.

But fundamentally, I think you're addressing an issue with my suboptimal framing of the puzzle, rather than the puzzle itself. I'm not really interested in the time trend (increase?) of the polarization of politicians. From the perspective of MVT, it's surprising that there are any differences between the two main candidates' positions, irrespective of the amount of polarization in the electorate. Certainly it's surprising that when elections are close, politicians don't move further towards the center in order to win - something must be restraining them. What is it?

I agree individual politicians could be irrational (in the sense of not optimizing for getting elected, though the precise mechanism still interests me). For example, maybe they do not change their true ideological positions to appeal to voters even when getting elected is at stake (is this likely?). But you'd still need to explain why other politicians, whose views are genuinely more moderate, don't emerge and win the elections. In the same way that individual producers and customers could be biased/selfish, but the market could still end up efficient & useful, the political system could have generated the most electable politician, who is a moderate. Why doesn't it? I can't think of any hypothesis not listed or raised so far.

I very much agree this is possible, if voters vote in primaries based on ideological proximity rather than electability. But then how come the national elections are close? Coincidence? And what would happen if a politician moved a bit more towards the center after winning the primaries?

This is an interesting explanation. But then how do you think voters enforce their views to make politicians more radical? Suppose there were general elections between two candidates, and then a voter's preferred candidate made his views more moderate to appeal to a larger audience. Would the voter not vote at all in these elections? Or would that politician just not pass the primaries? Otherwise, even if voters dislike it, a politician could still get elected while being less liked than they could have been by their party's voters, but importantly - win the elections.

Interesting. And how do you think they enforce this dislike of moderates? By not voting at all? By voting for the other party if it's more extreme? If they prefer extreme politicians but still vote for the politician closest to their views, the puzzle isn't solved.

Not sure I understand how this explains the polarization of politicians. What is preventing Biden from saying "Abortion is a state issue"? His tribe will still support him, but some fraction of the swing voters will find him more appealing. Couldn't it sway the elections in his favor? Why didn't he do it? Generally I don't see how tribalism is a challenge to the thesis.

That's interesting. I agree I glossed over many (most) parts where the parties agree (on general democratic principles, on capitalism in some form, on the order of magnitude of budget for many things) and focused on issues where they disagree.

But I think for my thesis, any remaining differences are a puzzle to be explained, and the perceptions that the parties differ is what drives the results. Since public debate focuses on issues where parties differ substantially, these should be the issues driving voting behavior - you can narrow down the model to those issues and still try to explain the puzzle, right? If voters don't perceive a difference between the parties, what is driving the changes in voting between different election cycles?

Thanks for the thoughtful comment!
I agree that the normative parts were the weakest in the Book. There were other parts that I found weak, like how I think he caught the Moral Foundations and their ubiquitous presence well, but then made the error of thinking liberals don't use them (when in fact they use them a lot, certainly in today's climate, just with different in-groups, sanctified objects, etc.). An initial draft had a section about this. But in the spirit of Ruling Thinkers In, Not Out, I decided to let go of these in the review and focus on the parts I got a lot out of.

I'll take a look at Greene, sounds very interesting.

About what to do about disagreements with conservatives, I'd say if you understand where others are coming from, perhaps you can compromise in a way that's positive-sum. It doesn't mean you have to concede they're right, only that in a democracy they are entitled to affect policy, but that doesn't mean you should be fighting over it instead of discussing in good faith.

I liked the final paragraph, about how reason slowly erodes emotional objections over a long time. Maybe that's an optimistic note to finish on.

Thanks!
I think you'll very much enjoy the part of the book about the hive switch, and psychedelics.