I'm not sure that's true in general. e.g. at around 300k the effective income tax rate in CA is ~34% (26% + 8.0% state) +5% (SS etc.) = 39%. That's quite low by European standards, if you go down to 150k the total is just 35%.

In Germany for instance you'd already be paying ~42% on 100k

Anyway, that wasn't my point at all, I'm just unsure how politically feasible it would be to accomplish this on the federal level.

> European Socialist Democracies

There is not a single country in Europe left which would describe itself as a "socialist" democracy (thankfully most of them collapsed around ~1990).