Tofail Ahmed helps a motorist at a BP gas station in Hoboken, N.J. A state ban keeps customers from pumping their own gas — which preserves about 9,000 jobs. (Julio Cortez/AP)

President Trump has made a huge deal of his attempts to bring back blue-collar manufacturing jobs that have gone overseas and to shame companies into building plants here rather than in other countries. Both of which I think are fine.

But Trump would probably get greater value for working-class Americans — and for American consumers — by spending some of his time leaning on companies to preserve a huge, threatened class of blue-collar jobs: cashiers. Yes, cashiers.

Speaking up for cashiers, which the Bureau of Labor Statistics says is the second-largest occupation in the country, wouldn’t be as glamorous or tweet-able as berating Ford or General Motors or Carrier for the loss of American jobs.

But it would be a great way for him to get back to playing offense and showing he cares about the working class. Supporting the nation’s 3.5 million cashiers could help preserve the livelihoods of hundreds of thousands of low-paid people who are in entry-level jobs or rehabilitating-themselves jobs or trying-to-feed-their-family jobs.

What’s more, there’s even an example, not far from Trump Tower in New York, of how preserving cashier-type jobs could be done, at minimal (or perhaps no) cost to consumers. It’s in my home state of New Jersey, which has saved thousands of such jobs — those of gas station attendants.

It’s the unintended but welcome outgrowth of the state’s 1949 ban on the self-pumping of gasoline, which many out-of-staters ridicule. Even so, it is so popular that Jersey residents have resisted repeated attempts to end it.

Now, let’s step back a bit.

The number of cashier jobs — No. 2 only to retail sales clerks, according to the BLS — was almost exactly the same in 2015 (the most recent year for which statistics are available) as in 2005, even though total U.S. employment was up by 7.6 million.

Still, it’s obvious that these jobs are threatened as never before.

Go into any large, reasonably modern supermarket, drug store or retail store, and you see more and more self-checkout lines and fewer and fewer manned cashier lines.

McDonald’s is using self-checkout in some locations. Even Costco — a big company that seems to care about employing people — is experimenting with it.

And here’s the crowning blow. Amazon, which has upended America’s retail business (and whose chief executive, Jeff Bezos, owns The Washington Post), is building physical stores that have no cashiers. If Amazon’s initiative succeeds, can cashier-less days at mainstream operations be far behind?

Look, I’m not proposing that the United States turn into a modern-day version of old-style Russia, where it took half a dozen people to check you out of a store. And I’m not proposing to return to pre-bar code days, when checkout lines were slower and there was more work for cashiers.

But I just look at the gas stations in New Jersey and compare them with the large, modern retail outlets in Atlanta’s northern suburbs, where my wife and I recently spent considerable time.

Georgia customers using the self-checkout line got no savings whatever in return for doing the store’s work. Late at night, at least some big stores had so few cashiers on duty that self-checkout became the norm.

By contrast, at New Jersey gas stations, someone pumps my gas. That’s a boon to those of us, like me, who have arthritic wrists that don’t react well to pumping my own gas, which I did in Georgia. And the Jersey gas lines moved more quickly.

Sal Risalvato, executive director of the New Jersey trade group that represents gas stations and convenience stores, estimates there are about 9,000 gas-pumping jobs in the state. (The BLS once tracked Jersey gas-pumping jobs but no longer does.) Risalvato, who wants the self-pumping ban repealed, estimates that having attendants increases the price of gas by about 10 cents a gallon. To put that in context: The state increased gas taxes by 23 cents a gallon in November, and the recent average cost of gas ranged from $2.32 a gallon for regular to $2.79 for premium, according to GasBuddy.

Robert Scott III, a professor at New Jersey’s Monmouth University who in 2007 published a scholarly article about the self-pumping ban, thinks it adds little or nothing to gas prices. A major reason, he says, is that insurance costs for Jersey gas stations are lower than they would be if customers pumped their own gas.

To be sure, you don’t see the plight of cashiers portrayed nightly on cable news, and there’s no big public fuss made when cashier jobs quietly slip away. But if Trump can dig out of his current problems and get back to playing offense, he could do a lot of good for cashiers and himself by publicly leaning on retail chains to preserve those jobs or even add to them.

And who can say? Just as we Jerseyites appreciate having gas pumped for us, store customers across the country would probably come to appreciate cashier-based checkout. We’d keep cashiers working instead of having to live in poverty or go on welfare or file for disability. We’d all win. And so would Trump.