Tyler's piece on Europe also lays down a challenge to American social democrats:
They [social democrats] think that enough changes would make America enough like Europe; I do not understand their underlying model of the differences between America and Europe, and thus I think they are badly wrong. Policy is not an exogenous or all-determining variable.
Frankly, I think the social democrats have a straightforward and better model than Tyler does: Europe is more social democratic than the U.S. because public opinion is more social democratic in Europe than the U.S. Period. Objective differences may have some small influence on public opinion, but not much.
Furthermore, who ever said that policy was exogenous? My model, and I suspect that most social democrats agree, says that policy is determined by public opinion. It's public opinion that seems exogenous, not policy.
The key disagreement between me and the social democrats that Tyler criticizes: The social democrats think that Americans underestimate the wonders of social democracy. I think that Americans severely overestimate social democracy, and Europeans are even more mistaken.