adding new marginal tax brackets above the current top level ($357k)

Yglesias proposes adding new marginal tax brackets above the current top level ($357k). While he minimizes the potential for raising significant revenue this way, Nate Silver starts the math and finds otherwise:

What the discussion over the top marginal tax rate ignores, however (and what Ygelsias picks up upon) is that this rate has been assessed at very different thresholds of income. In 1940, for example, the top marginal tax rate was 81.1 percent -- but this rate only kicked in once you made $5,000,000 or more in income, which is equivalent to about $75,000,000 in today's dollars.

But today, the threshold where the top tax bracket kicks in isn't $75 million, or $5 million, or even $1 million ... it's a mere $357,700. The progressivity of the tax code stops there....

The question, of course, is why there isn't a millionaires tax bracket now ... or even a multi-millionaires tax bracket. I haven't run the numbers, but I'm guessing that if you established a new tax bracket at, say, 40.5 percent, that started at incomes of $1,000,000 or more, this would bring in as much revenue to the government as restoring the $250K tax bracket (which is really $360K now given indexing to inflation) to 39.6 percent, as it was under Clinton.

Clive Crook gives the rationale for creating new upper-level brackets -- though he himself favors the regressive but broader-based VAT:

Not everybody would regard two-earner households with an income of $250,000 a year as rich; and many of the taxpayers in question have seen their retirement savings, college funds and housing equity destroyed. The scandal of widening inequality that still animates the Democrats' thinking is a story about the top fraction of one per cent of the income distribution, not the top end of the middle class.