One of the most popular proposals on the table from Democrats heading into the 2020 primaries is Elizabeth Warren’s proposed “wealth tax” that would hit millionaires and billionaires. It’s become so popular that even 50% of Republicans somehow endorsed it in a recent survey. The attraction to such a plan among populists is obvious. It would generate some measure of revenue for the federal government (though not nearly as much as many liberals seem to imagine) while not taking a dime out of the pockets of most of the people voting for it. It’s a chance to spend other people’s money

But is such a scheme even constitutional? That question is addressed by Jonathan Turley at the Washington Post, and while there isn’t a definitive answer to the question available, it’s really not looking good for Warren and her ilk. There is some precedent on both sides of the debate, going all the way back to the days when Madison battled Hamilton over the extent of federal governmental power, but he makes a good case for any wealth tax falling outside Washington’s powers of taxation.

As she officially kicked off her presidential campaign last weekend, Sen. Elizabeth Warren rallied her supporters behind her signature proposal: a wealth tax on the rich. The Massachusetts Democrat wants an annual charge of 2 percent on the holdings of anyone with more than $50 million in assets. Billionaires would be subject to a 3 percent tax, to “make sure rich people start doing their part for the country.” Polls show that Warren’s “ultra-millionaire tax” is overwhelmingly popular, with 60 percent of voters favoring it, including a majority of Republicans.

It is also probably unconstitutional. A legal challenge against it would immediately rekindle a debate first argued by James Madison and Alexander Hamilton. Our founding document says the federal government can levy only a few, very specific kinds of taxes. Warren’s plan is outside the rules.

Turley’s analysis is a bit of a deep dive, but definitely worth the time to read if you’re going to be following the battle to come. (At some point the Democrats will retake enough power in Washington to try this and it clearly looks like they won’t be able to resist the temptation.) But here are a few of the highlights.

Turley notes that the federal government is actually quite limited in what sorts of taxation they can impose, or at least they are in theory. The 16th Amendment assured they could impose taxes on income, but beyond that, we get into some gray areas. The Constitution gives Washington the power to lay and collect taxes, duties, imposts and excises. But it also goes on to say that Congress cannot impose any “capitation, or other direct tax” unless it’s uniform across the states and in proportion to the results of the decennial census.

There’s been a running debate about what constitutes a “direct tax” for a very long time, and Congress (with the help of the courts) has used all manner of verbal legerdemain to get around these restrictions. But hopefully, there are still limits. As Turley points out, Hamilton and Madison argued over a tax on carriages in 1794, with Madison saying it was a direct tax and therefore not in keeping with the Constitution. Hamilton countered that it was an excise tax on purchases (specifically the purchase of a carriage) and the courts agreed with him. But Hamilton poisoned the well for Warren’s plan because a “wealth tax” on all assets wouldn’t fit his criteria.

It would seem that the only way to justify a wealth tax would be to argue that the basic definition of the word “tax” has changed over time and previous courts got the concept of a “direct tax” wrong. And that argument has been made by people trying to bolster Warren’s plan. But if we allow that to happen, then we’ve thrown the Constitution out the window and opened the doors to Congress taxing pretty much anything and everything they please. (Not that they don’t do that to the best of their ability now under a variety of excuses, but this would make it worse.)

We can forget for the moment that such a tax would be a major disincentive to growth and investment by the successful. This plan should be rejected just out of respect for the nation’s founders.