America invented progressive taxation. And there was a time when leading American politicians were proud to proclaim their willingness to tax the wealthy, not just to raise revenue, but to limit excessive concentration of economic power.

“It is important,” said Theodore Roosevelt in 1906, “to grapple with the problems connected with the amassing of enormous fortunes” — some of them, he declared, “swollen beyond all healthy limits.”

Today we are once again living in an era of extraordinary wealth concentrated in the hands of a few people, with the net worth of the wealthiest 0.1 percent of Americans almost equal to that of the bottom 90 percent combined. And this concentration of wealth is growing; as Thomas Piketty famously argued in his book “Capital in the 21st Century,” we seem to be heading toward a society dominated by vast, often inherited fortunes.

So can today’s politicians rise to the challenge? Well, Elizabeth Warren has released an impressive proposal for taxing extreme wealth. And whether or not she herself becomes the Democratic nominee for president, it says good things about her party that something this smart and daring is even part of the discussion.