President Trump loves tariffs. And he's slapping them on China, Europe, and anyone one else who gets on his bad side.

When you think about this, it's actually really strange. Tariffs are taxes, and the Constitution very clearly gives taxing power to Congress. Presidents have to sign off on these laws, of course, but it's Congress that writes and passes them. Yet there's Trump, unilaterally jacking up duties on steel, aluminum, and other goods without any input from the legislature whatsoever.

How can he do this?

The short answer is that Congress slowly ceded tariff power to the president over the last 80 years or so. Way back when, all sorts of regulatory and lawmaking activity was handled far more directly by the legislature. But the period leading up to and after the New Deal marked a sea change in U.S. politics, with Congress handing much responsibility over to various executive agencies. Tariffs were no exception.

A variety of laws — including the Trading with the Enemy Act of 1917, the Tariff Act of 1930, the Trade Expansion Act of 1962, the Trade Act of 1974, and the International Emergency Economic Powers Act of 1977 — had the same basic framework: Congress would lay out the circumstances that would justify a tariff, and then say that if the executive branch did its research and issued a finding that those criteria were met, it could go ahead and impose the tariff. This gave the president an enormous amount of leeway.

But why did Congress do this?

For one thing, as America grew to become a global player, international trade issues inevitably became tangled with foreign policy — and the Constitution gives the executive far more power in the latter field. Detailed oversight of tariff policy is also hard. At one time, Congress "had to negotiate individual tariff rates on every product under the sun," Todd Tucker, a political scientist at the Roosevelt Institute, explained to The Week. This led to endless and time-consuming hearings. As a result, America spent the 1800s with barely any trade agreements at all, save a brief one with Canada and another with pre-state Hawaii. Semi-automating the process by handing responsibility over to the executive and its agencies helped streamline American trade policy.

Now, the powers Congress delegated to the presidency are quite broad. For instance, Trump has relied heavily on Section 232 of the Trade Expansion Act of 1962. It gives the president the power to levy tariffs to meet "national security" needs. As much of the press (including myself!) has said, Trump's use of Section 232 has been so expansive that no one really buys the national security rationale. But Tucker explained that the plain language of Section 232 is actually incredibly broad; its writers pretty clearly understood "national security" to encompass America's various economic and industrial advantages. "The people that passed 232 would've been at home, I think, with some of the stuff Trump's been doing," Tucker said.

There's clearly been something of a national attitude adjustment on these issues, too. "From a constitutional point of view, trade wars are like shooting wars," Timothy Meyer and Ganesh Sitaraman recently wrote at Lawfare. "Our Constitution gives Congress power over the initiation of both. But in the 20th century, a belief that the president is more capable and efficient in managing the nation’s foreign affairs — and more likely to reach particular policy outcomes, such as lower trade barriers — led Congress to cede ground to the president."

Prior to Trump, every president since FDR more or less agreed with American elites' bipartisan consensus in favor of more globalized trade. To the extent executive tariff threats were used in the 1970s and 1980s, it was a negotiating tactic to drive bargains for more globalized trade and lower barriers all around. No one really worried that such enormous power was being handed over, and the U.S. president's unilateral ability to launch a trade was left unused.

Then came Trump, and a new obsession with trade wars.

In some ways, this was inevitable. The executive's unilateral trade power arguably allowed the globalized trade push to get out way ahead of what many Americans were actually comfortable with. And backlash against that whole arrangement certainly helped fuel Trump's rise. As Meyer and Sitaraman point out, running tariffs and trade policy through Congress may be messy and ungainly, but it also gives the many regional and industrial interests across the country a chance to have their say. The status quo also allows the executive branch to conduct trade policy with far more secrecy and much less transparency than, say, environmental regulation, where new rules have to go through a whole public comment process.

But at this point, can anything be done to restrain Trump's tariff spree? Probably not.

Congress would have to pass a new law to roll back the president's authority. But they'd need overwhelming support to override an all but assured presidential veto. And Republicans are loathe to directly confront Trump on this issue. As a result, something like Sen. Mike Lee's (R-Utah) Global Trade Accountability Act probably isn't going anywhere.

Sen. Bob Corker (R-Tenn.) is trying a slightly different route: He's got an amendment that would require congressional authorization for any tariffs imposed under Section 232. And he's trying to slip it in under the radar by attaching it to some bigger must-pass legislation. But so far the Senate's latest military spending authorization and its version of the farm bill have come and gone, and Corker wasn't able to get the amendment into either.

Finally, someone could sue to stop Trump's tariffs. But courts don't like to question the president's prerogatives when it comes to national security and foreign policy. A new lawsuit is trying a different tack: It's arguing that Congress' delegation of authority to the president was itself unconstitutional. Since this Supreme Court seems eager to roll back the New Deal, the suit relies on the fact that current presidential trade power was part and parcel of the New Deal shift. But the suit was only just filed, so we'll have to wait and see.

For the foreseeable future, presidential trade power — which Congress created to restrain protectionism — remains unchecked. And it now rests in the hands of Donald Trump, arguably our most ardent protectionist in a century.