Donald Trump’s top economic advisers don’t want you to know this, but the only way he can fulfill his promise to get the economy growing at 3% to 4% is to give more jobs to Mexicans.

It’s a matter of economics, demographics and arithmetic.

There are only two ways to get the economy to move faster over a sustained period: Hire more workers, or make the workers we have more productive. Those two factors — working harder and working smarter — determine the economy’s potential growth rate, or its speed limit. Potential growth is the sustainable level of output that the economy can supply, and right now it’s below 2%.

Here’s the economic equation: Potential growth = labor-force growth + productivity growth.

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Unless we can magically get productivity to improve at the fastest rates in the past 50 years, the only way to get to the gross domestic product to grow at 3% on a sustainable basis would be to hire 33 million workers over the next 10 years. The problem? With the working-age population barely growing, the supply of qualified and willing Americans to hire would quickly run out, which means we’d need to open up the borders and let more immigrants in.

In 2020, for instance, the working-age population is expected to grow by about 600,000, according to the Census Bureau. But to grow GDP at 3%, the economy would need 2.8 million more workers that year, even if productivity rebounds modestly, as assumed by the Congressional Budget Office in its projections about potential growth.

Of course, if Trump has his way on restricting imports from Mexico, there will probably be quite a few unemployed Mexican workers who’d be glad to trek north to take those jobs.

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To put this in some perspective, the largest job growth over any 10-year period in our history was 22 million from 1972 to 1981. We added just over 20 million from 1992 to 2001. In both periods, the working-age population was growing about four times faster than it will over the next 10 years.

Trump’s economic team — Steven Mnuchin, who would be the Treasury secretary, and Wilbur Ross, who would be the commerce secretary — went on cable TV on Wednesday to make a lot of promises about how huge the economy will be under President Trump.

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Mnuchin, a hedge-fund operator and former Goldman Sachs partner, said Trump would “create huge economic growth,” and said we could “absolutely get to sustainable 3% to 4%” growth under Trump.

Mnuchin said the American economy would soar after Washington slashes corporate taxes, rewrites the trade rules and deregulates industry after industry, from coal to banks.

Now, those ideas might be good for the economy, depending, of course, on the details and the implementation. We all know the corporate tax code is an inefficient mess, we all know our trade deficits are far too high, and we all know there are some regulations that are too costly for what they deliver.

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And we all know that fixing these things is a lot harder than going on TV to talk about fixing them.

But even if Trump does all those things, the economy still won’t be able to grow at 3% or 4% on a sustainable basis.

Facts and figures

How do we know? From studying basic subjects like arithmetic, history and economics.

Here’s the history lesson: The economy was able to enjoy rapid growth in the past when the labor force was growing rapidly, as it did from the late 1960s through the 1980s, or when productivity was improving rapidly, as it did in the 1960s and late 1990s.

But now, the potential labor force is barely growing, and productivity is in the dumps. The economy’s potential growth rate has fallen from more than 4.5% in the late 1960s, to 3.5% in the Reagan and Clinton years, to just 1.6% now.

That’s only half the growth rate that Trump is promising.

Unfortunately, there’s very little that Washington can do change potential growth in four or even eight years. It takes more than a slogan. Sure, politicians can stimulate the economy and make it grow faster temporarily by creating more demand through tax cuts and more spending, but that doesn’t change the economy’s capacity to produce.

In the longer run, the constraint on growth isn’t the level of demand, it’s how much our economy can supply. The real key to faster growth (and higher living standards) is to increase the economy’s productivity. That means more capital invested, better technology and more skilled workers.

Trump’s brains know this. That’s why they claim, absurdly, that tax cuts, trade reform and deregulation will magically transform the supply side of the economy, by boosting investment in the tools and ideas that will make our economy more productive.

If they were well-designed and implemented, Trump’s supply-side policies probably could do some good in that regard. Better public infrastructure, more private investment in structures, machines and software, and more research and development would probably pay off. But the gains wouldn’t be nearly enough to get us to 3% growth, if history is any guide.

If the labor force is growing at only 0.5% per year (which it will be for the foreseeable future unless there’s lots more immigration), then productivity would need to improve 2.5% every year to reach 3% growth (0.5% + 2.5% = 3%). It would have to hit 3.5% to reach 4% growth.

Tax cuts, deregulation won’t do it

Unfortunately, we’ve hit 2.5% in a single year only three times in the past 20 years, and each of those productivity bumps followed a recession that temporarily depressed productivity. The last time the economy managed a sustained 2% productivity improvement was the mid-1960s.

Trump’s team is crowing that the tax cut they propose will be the most sweeping since the 1986 tax reform. And how did productivity do following that tax reform? Over the next five years, productivity growth averaged 0.4%. Over the next 10 years, it averaged 1%.

The track record for supply-side tax cuts and deregulation isn’t great. Trump’s team claims that deregulation will unshackle American businesses and deliver huge growth, but those estimates are based on particularly dubious fantasies that completely ignore the benefits of regulations.

Trump’s team has forgotten the terrible cost inflicted on the economy by the deregulation of the financial sector (which helped to reduced Trump’s own empire to ashes in the early 1990s) and which culminated in the trillions of dollars of economic output lost globally over the last decade after the deregulated financial sector caused the greatest economic crisis since the 1930s.

Even if Trump can implement all his ideas perfectly, he won’t be able to raise American productivity enough to get to 3% growth. That would leave massive immigration as the only path to the faster growth he’s promising.

I don’t think that’s what Trump’s supporters voted for.