In the last couple years, the financial transactions tax (FTT) has moved from a fringe idea to a policy proposal treated seriously by even the mainstream of the Democratic Party. The decision by Senator Bernie Sanders to make it a central part of his presidential campaign certainly helped, but a number of members of Congress, including Keith Ellison and Peter DeFazio, have also pushed FTT proposals for many years.

The FTT is also gaining momentum overseas. There’s a push to enact an FTT in the eurozone. And in England, an expanded FTT — the London stock exchange has long levied a 0.5 percent tax on stock trades — was included in the Labour Party’s platform in the recent election.

But while the idea of taxing financial transactions is growing more popular, even many of its proponents don’t realize its full benefits. An FTT is usually seen as a way to raise large amounts of revenue (in the US, it could possibly generate as much as $190 billion a year, or 1 percent of GDP). Or it is viewed as a means to limit speculative trading in the financial sector, potentially making markets less volatile.