Well, it was bound to happen eventually. After near three years of all-out rhetorical war against tech giants, for politically-shifting sins including bigness, too much censorship, not enough censorship, data hoarding, and being too irresistible, policymakers are ready to move beyond cheap talk and start slapping wrists—or more.

Specifically, regulators and Congress recently announced new antitrust scrutiny against Silicon Valley. The House Judiciary Committee cheerfully launched a "bipartisan investigation into competition into digital markets." Nothing can bring us all together these days quite like hating the online services we use most. No particular firms have been named, but we can expect the usual suspects are due for a thrashing.

Regulators, on the other hand, are dividing and conquering. The Department of Justice (DOJ) and Federal Trade Commission (FTC) sliced up the pig, with DOJ taking on Google and Apple, and the FTC going after Facebook and Amazon. The Wall Street Journal reports that Google and Facebook are the real targets, for now.

Tech companies knew this was coming. How could they not? Presidential hopefuls compete over who wants to break up tech giants the most. New books like The Curse of Bigness: Antitrust in the New Gilded Age by superstar law professor (and father of "net neutrality") Tim Wu warn that lax antitrust enforcement could spawn a new Nazism (really). In February, the FTC set up an antitrust taskforce for the sole purpose of preparing actions against the big guys. It was always a question of when, not if.

Bigness is badness in the minds of most people. But in terms of U.S. law at least, being big is not a crime.

Rather, as an essay by my Mercatus colleagues Adam Thierer and Jennifer Huddleston points out, American antitrust is only intended to be used when "a firm has the ability to monopolize a sector, or it possesses an 'essential facility' that cannot be replicated."

Laws like the Sherman Antitrust Act and the Clayton Act give agencies substantial powers to clamp down on monopolies. So antitrust enforcers have developed a robust jurisprudence on what is and is not kosher. Some things, like price fixing, are so "inherently harmful" that they are always illegal.

But in general, the U.S. antitrust approach places the consumer at the center of the analysis. We don't punish businesses because they have been exceptional at meeting consumer demand. Rather, the government steps in if a business engages in anti-competitive activities that harm customers, like obliterating the competition with low prices before jacking them up on consumers that have no other option—classic monopolistic behavior.

Doesn't that just make sense? Consider the alternative. The government could break up or limit any firm that is simply a great competitor. Consumers are actually served well by this giant. But their competitors of course will grumble for their nemesis to be taken down a few pegs.

In this conception of antitrust, the government essentially protects the bottom lines of competitors who can't keep up. Before U.S. courts settled on the economics-grounded consumer welfare standard that has guided U.S. antitrust for decades, trust-busting activities were often little more than handouts to interest groups.

Not only would court cases counterintuitively seek to keep prices high, to the detriment of consumers, judges worked a host of non-antitrust hobbyhorses into their decisions. Maybe one judge had a particular fondness for "social equality." The antitrust decisions he handed down might have aimed for that totally unrelated, arguably impossible outcome.

The European approach to antitrust is more like the muddled U.S. approach before it settled on the consumer welfare standard. Some in the U.S. would like our antitrust posture to be more like Europe's, but at least for now, it is limited to the scribblings of theorists in the land of the free.

With that crash course in antitrust theory under our belt, we can now ask: What will the U.S. do about Facebook and Google?

Some people would like to see the companies broken up. They propose surgical cuts: Facebook must relinquish WhatsApp and Instagram, while parent company Alphabet could spin off feeder products from advertising-funded search.

On what grounds? We know that bigness per se is no crime. Are these companies "essential facilities" that left fewer, more expensive options for consumers?

The problem is that many of these companies' products cost us nothing, at least in terms of dollars. It doesn't look like Facebook or Google have been lowering product quality, either. In general, there's a lot of competition when it comes to social media platforms and search, even if people choose not to use them very much.

Online platforms like Facebook and Google are tricky when it comes to antitrust because they essentially serve two markets: users and advertisers.

When it comes to users, there are plenty of alternatives. Advertisers, too have plenty of alternatives: they can buy spots on television, the radio, billboards, in newspapers, and even via costumed sign-waver on the side of the road.

But for online ads, there are basically two games in town: Facebook and Google. My colleague Brent Skorup pointed out to me that recent precedent could indicate that the courts will consider "the ad market and the social media market as components of a single relevant market." If so, Facebook and Google could be looking at serious antitrust enforcement.

But will this brouhaha end up being irrelevant?

Antitrust actions take a long time, and by the time a remedy—good or bad—is chosen, the market may have already moved on. This is particularly the case in a fast-moving space like tech. Consider the drawn-out cases against IBM and Microsoft. On the other side of the decades-long court cases, the issues that so vexed regulators had long ago become moot. What were the costs to consumers and innovation in the process?

The problem is that regulators have a static mindset. They see a slice of a market in time, deem one actor too powerful, and seek to artificially create "more competition" to freeze this market in time. But that's not how markets progress. As venture capitalist Benedict Evans points out, "Tech anti-trust too often wants to insert a competitor to the winning monopolist, when it's too late. Meanwhile, the monopolist is made irrelevant by something that comes from totally outside the entire conversation and owes nothing to any anti-trust interventions."

In the meantime, antitrust actions are often wasteful, distracting, and can limit consumer choice. We still don't how this new round of trust-busting will shake out. But it's a good chance that by the time we're on the other side, a new class of unassailable giants will have cropped up without regulators noticing. And then we can start the theatrics all over again.

This column has been updated to correct Tim Wu's occupation.