Maybe you don’t remember where you were on Tuesday, April 1, 1980. But I do. I wasn’t getting married. I wasn’t climbing Mount Everest. I wasn’t counting my money after winning the lottery.

No, I was on a more captivating quest — following U.S. census takers as they tried to find every last person living in Rochester, N.Y., as of that year’s “Census Day.” As a reporter in Rochester assigned to cover the decennial national head count months before, I had had no idea what an adventure it would be.

Census takers followed dirt paths to find homeless people living beneath bridges that span the Genesee River. They recruited some of the dispossessed to help locate other makeshift shelters. An army of census takers climbed the stairs of rundown apartment buildings, where the poor lived without luxuries — or telephones. They ventured into flophouses to find the town drunks.

They knocked on the doors of houses that, somehow, weren’t in the city directory. They tapped on the windshields of cars that some people had made their homes. Across the country, census takers visited rural shanties that were the temporary addresses of migrant workers. They totaled the millions living behind bars — visiting jails and prisons to ensure that no U.S. residents were overlooked.

In the end, the 1980 census counted 226,545,805 souls, millions of whom lived in the shadows — among us, but apart. No drops were overlooked in measuring the sea of humanity.

But the 2020 census may mark an abrupt turn in the way a nation of (now) an estimated 335 million will be tallied. For the first time in the history of the republic, the Census Bureau plans to go out of its way to ensure millions of U.S. residents aren’t counted. Deliberately. With malice and forethought.

In an epic act of government malpractice — likely to be allowed by the conservative majority of the U.S. Supreme Court in a ruling expected this month — residents will be asked whether they are U.S. citizens. A question phased out of the census 70 years ago. A question reintroduced to drive undocumented immigrants underground for dread of being jailed or deported. Millions of U.S. residents, by design, will remain out of sight, out of mind and out of luck. The 2020 census is being sabotaged.

In Donald J. Trump, the nation has a president who doesn’t read. Who doesn’t know how to spell. Who doesn’t know arithmetic. He is a president trying to ensure that people he thinks don’t count aren’t counted.

The 2020 census represents Trump’s latest act of political vandalism. The idea is to diminish the political clout of Democratic strongholds — states with large immigrant populations. How? Make sure immigrants fear answering the call of the census.

Trepidation makes sense, given Trump’s draconian attacks on undocumented immigrants. What’s to prevent self-identified noncitizens from being reported to immigration police? Certainly not Trump.

States with significant immigrant populations will end up with billions less in federal aid and a weaker voice in Congress.

Census experts estimated the “citizenship question” would not only make the 2020 head count less accurate but add $121 million to the cost of the census. Trump’s apparatchik, Commerce Secretary Wilbur Ross, ignored the warnings.

It’s a naked power play by a White House not all that committed to the principles of democracy.

But leaving millions uncounted also is an attack on the economy — depriving tens of thousands of companies the information they need to do business effectively.

Trump, revealed in leaked IRS reports to be the most unsuccessful business operator of his generation, appears blissfully unaware of the damage he’ll do to firms run by competent executives.

In modern commerce, the census isn’t a quaint constitutional curiosity. It’s a crucial tool.

Businesses need to know population trends (age, sex, race, income and educational attainment) — gleaned from the census — to decide where to locate factories, warehouses and corporate offices.

It’s called due diligence.

The kind of research that Trump, who drove casino after casino into bankruptcy, apparently failed to do.

What’s the age and condition of the local housing stock? That census data could inform where Home Depot or Lowe’s locates its next big-box store. How would home-remodeling companies know where to advertise without census numbers?

New firms, such as Uber and Lyft, rely on the census to locate neighborhoods that are the most likely to yield customers and drivers.

HMO medical clinics, hospitals, schools (public and private) make location decisions with the help of the census.

An inaccurate census — overlooking as many as 6.5 million Latinos and immigrants — would leave many executives flying blind.

Sort of like Trump Shuttle, a once-thriving airline service between New York, Washington, D.C., and Boston. Trump plunged it into the red, then sold it at a loss to get out under some of his outsized bank debt. Who needs to do research? A “stable genius” goes with his gut.

Thankfully, others aren’t so cavalier.

But without reliable census numbers, a machine shop wouldn’t know where to recruit pools of skilled labor. Owners of day-care centers would be unable to find neighborhoods with large pockets of children under age 6. Assisted-living providers would be hard-pressed to find where seniors are clustered. News flash: Immigrants have children and get old, too.

“We don’t view this as a political situation at all,” says Christine Pierce, the senior vice president of data science at Nielsen, told NPR. “We see this as one that is around sound research and good science.”

Consequences of an inaccurate census threaten national industries as well as local ones.

“If there is an undercount, that could carry through to our audience estimates and could mean that people will make decisions based on data that isn’t as accurate as it should be,” Pierce said.

TV ratings data, by Nielsen’s estimate, are tied to $90 billion in TV and video advertising.

“There’s just no substitute for a good census and having that count be as thorough as possible,” Pierce told public radio.

Sophisticated business executives rely on the census to answer all manner of questions that affect the bottom line. Census figures aid in targeting high-income consumers for luxury goods, for instance, giving companies an idea not only where potential customers live but how much they can afford to spend.

Had Trump performed that kind of careful research, maybe he wouldn’t have bought the Plaza Hotel at a price so inflated that he couldn’t pay the mortgage even if every room was rented, every night, at full price. Ultimately, he sold the hotel for $83 million less than he had paid to buy it.

Ironically, successful real estate players rely on census numbers to make sound decisions. Apartment developers and homebuilders scour the census for information on household formation, housing vacancies, household affordability, and other metrics that drive supply and demand.

Census numbers are employed to build forecasts that steer investment from one part of a city to another or from one region to the next.

What good are forecasts if they leave out millions of immigrants who need places to live, to shop, to play?

Trump, who reportedly lost more than a billion dollars from 1985 to 1994, may not use or understand such research. Losing more than twice as much as any U.S. taxpayer during the period requires a disregard for reality that few others possess.

In the 2016 presidential campaign, Trump promised to run the country like one of his businesses. By undermining the next census and crippling the ability of private investors to make informed bets, the president is delivering on that promise.

Mike Meyers, a former Star Tribune business reporter, is a writer in Minneapolis.