The best estimates I have seen indicate that Sanders is advocating for a maximum effective marginal tax rate of about 70 percent, which gives rise to two questions:
1. Is this rate historically large? Compared to rates in the during the Eisenhower Administration, not at all. However, we haven’t seen rates like this since the 1980’s, and capital is a lot more mobile now than it was then.
2. How does this rate compare to those of other countries with reasonably similar economies? It would be very high. Recent experiments with “supertaxes” have been failures. Realistically speaking, you could expect a large increase in tax exiles, with a corresponding reduction in the dynamism of the American economy.
In short, I have no problem advocating for a country that looks a bit more like Denmark, but this is a bridge too far.