Once upon a time, our competition cops weren’t afraid of giants. Federal regulators broke up Rockefeller’s Standard Oil monopoly, kept DuPont from dominating military supply, and broke Ma Bell into what’s now Verizon and other pieces.

But it’s been popular, since the Nixon-Reagan-Clinton trade deals, to neglect old ways of measuring monopoly. If IBM, Exxon, GM, and DuPont have to compete with government-backed Chinese and European companies at home and abroad, does it make sense to punish them if some of their products are extra popular with U.S. buyers?

Break up JPMorgan Chase, the biggest U.S. bank, and you just invite government-backed Chinese banks to run the financial world, as its CEO, Jamie Dimon, argued in this space last week.

And scholars led by Robert Bork argued that big, dominating businesses are not bad if their prices are low for consumers. Sometimes big companies are the most efficient, cheapest suppliers. Even if their inefficient small-business rivals get crushed.

But as trustbusters napped — and the Obama Justice Department closed antitrust offices in Philadelphia and other towns — it should be no surprise there are now very few American suppliers of some basic products, such as insulin for diabetes, balloon helium, or bread and breakfast-cereal grains — and their rich owners are jacking up prices and reaping fat profits at consumers’ expense.

The Trump administration has vowed to do something about monopoly power — at least in the case of the big West Coast tech giants, whom the president and some of his supporters accuse of pandering to Democrats and liberals.

So Makan Delrahim, Justice’s antitrust chief (who formerly advised Apple and other big companies), and Joe Simons, chair of the Federal Trade Commission, met last month — at an antitrust conference in Cartagena, Colombia, Bloomberg reports — to divide the four top tech players and investigate them.

Justice is looking at the smartphone-maker and music-retailer Apple and the search-shop-advertise heavyweight Google, both of which have been slapped hard by antitrust enforcers from the European Union. Those blows include $9 billion in fines against Google for its exclusionary Android, shopping, and ad policies, and ongoing probes of Apple’s music and publishing market control.

Meanwhile, the FTC is reviewing the digital-shipping giant Amazon and social-media leader Facebook, and how they may “misuse their massive market power,” as Reuters put it last week, helping send their shares lower on the stock market.

The president has made a crude popular case for this crusade, alleging that Facebook’s and Twitter’s customer-exclusion policies have been used to punish conservatives. Trump has also complained about the close (and mutually profitable, both sides claim) package-delivery business relationship between the Postal Service and Amazon, whose boss, Jeff Bezos, also owns the Washington Post, famous for its scrutiny of presidents and government spending. Leftists make similar complaints that they are disproportionately targeted.

And why shouldn’t Big Tech be able to drop some folks? As privately owned communications networks and publishers, digital services aren’t subject to the common-carrier rules that force turnpikes, railroads, and landline phone systems to take all customers. They have a right to refuse your business for many reasons — and legal duties to refuse some. Don’t like their system? Choose another. Or build one.

But if these big private services have really become so powerful there are no effective alternatives, that’s something the government can address. Both Republicans and Democrats in Congress have held hearings and are actively investigating digital markets and Big Tech dominance. News publishers have lately asked Congress for special powers so they can gang up to win a better split of Google and Facebook ad revenues for our stories, which have so far enriched Big Tech at our expense.

“There is lots of pent-up demand, on both sides of the aisle, to investigate," says Michael Carrier, a scholar of competition and antitrust law at Rutgers Camden Law School. He says European cases punish giants who crush small competitors and business customers. It was the European Commission that two years ago forced Wilmington-based DuPont to sell pesticide labs and factories to Philadelphia-based FMC before joining with Dow Chemical to form farm-sales giant Corteva.

Successful U.S. antitrust cases tend to focus more directly on harm to consumers. So Justice and the FTC may investigate freely, but they are only likely to bring cases founded on solid legal arguments, Carrier concludes: “They won’t break companies up just because they are big.”

A Wharton School report last week warned that digital giants and the control and privacy issues they raise “don’t fall neatly under existing U.S. laws.”

Wharton information-management professor Eric K. Clemons sees a “very strong” case against Google, whose effective control of online search-and-buy, he told Knowledge at Wharton, has become so great that the company can charge retailers up to half the price of online-sales items for linking search keywords to their products.

Amazon is going further, “systematically dropping” small-business customers from its marketplace so it can better compete for their customers, Clemons added. “The abuse of small sellers does violate existing U.S. law, and that’s a concern.”

He also says Amazon’s Alexa digital home assistant can easily default to order from Amazon’s favored vendors (like Amazon’s own Whole Foods), giving the company an unfair edge.

There are downsides to aggressive monopoly-busting. Breaking up Big Tech could boost the price of services that companies like Google give away. It could allow those rival, government-backed, foreign companies to step fast into the vacuum, gaining dominant share in global communications, data, sales, advertising.

But a lot might be gained, if regulators can get big businesses to ensure U.S. start-ups and competitors fair access to crucial communications, data, and payment networks, so they can grow for the next generation.