The FBI’s argument is pretty simple. We’re the cops, they’re saying. We’re investigating an act of terror on American soil. It’s our job to pursue every lead. There may be evidence in the San Bernardino killer’s iPhone that will prevent future attacks. We can’t get to that information unless we figure out the phone’s 4- or 6-digit PIN. The phone’s operating system has made that impossible. We’re not asking Apple to create a backdoor. We’re not putting hundreds of millions of phones at risk. We’re just asking Apple to do three things, and just for this phone:

1. Disable the iPhone’s optional 10-tries-and-wipe feature
2. Remove built-in passcode delays (5 minute after 5 attempts, etc.)
3. Create the ability to enter PINs electronically, at computer speed, rather than the speed of thumbs

.

How hard could that be?

“Compliance with the order would not require inordinate effort,” the DOJ asserts. “Modifying an operating system—which is essentially writing software code in a discrete and limited manner—is not an unreasonable burden for a company that writes software code as part of its regular business.”

[Cue the groans of anyone who has ever written a line of computer code.]

Apple’s response is complicated, made more so because it includes Constitutional arguments (First and Fifth Amendment) that it will need if the case goes to the Supreme Court. Apple agrees that the San Bernardino attack was terrible, and it concedes that it has cooperated with the FBI in the past.

Otherwise it disputes every point.

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The FBI is asking for a way to get around the phone’s security features—which is, by definition, a back door. And it’s not just for this phone. If the government wins, this case will be cited as legal precedent in hundreds of cases going forward, just as the DOJ cites the 1977 ruling that ordered New York Telephone to give the FBI access to a suspect’s pen register (the file that contains the time and phone number of every call).

Apple also cites U.S. v. New York Telephone because the Supreme Court, in its ruling, addressed the question of what is and isn’t an “unreasonable” request under the All Writs Act. That’s the legal catch-all that gives police the power—lacking any other controlling legal authority—to enlist the assistance of an innocent third party. Not only is modifying an operating system a lot harder than the government makes it out to be—much harder than handing over a pen register. But if Apple (AAPL) can be compelled to write this code for the FBI, the company asks, what’s to stop the government from asking Apple to write code that will turn the iPhone into a surveillance device that can surreptitiously shoot video, record conversations or track a customer’s every move?

That’s pretty far fetched, and it’s an argument Apple may not need to win this case.

Apple’s strongest argument, it seems to me, is that Congress has already addressed these questions and answered them in Apple’s favor in a law called the Communications Assistance for Law Enforcement Act (CALEA).

Apple writes:

“Congress knows how to impose a duty on third parties to facilitate the government’s decryption of devices. Similarly, it knows exactly how to place limits on what the government can require of telecommunications carriers and also on manufacturers of telephone equipment and handsets. And in CALEA, Congress decided not to require electronic communication service providers, like Apple, to do what the government seeks here. Contrary to the government’s contention that CALEA is inapplicable to this dispute, Congress declared via CALEA that the government cannot dictate to providers of electronic communications services or manufacturers of telecommunications equipment any specific equipment design or software configuration.

“In the section of CALEA entitled ‘Design of features and systems configurations’ … the statute says that it ‘does not authorize any law enforcement agency or officer —

“(1) to require any specific design of equipment, facilities, services, features, or system configurations to be adopted by any provider of a wire or electronic communication service, any manufacturer of telecommunications equipment, or any provider of telecommunications support services.

“(2) to prohibit the adoption of any equipment, facility, service, or feature by any provider of a wire or electronic communication service, any manufacturer of telecommunications equipment, or any provider of telecommunications support services.”

For more on Apple vs. FBI, watch this video:

I could be wrong—and all five of the Republican candidates for President still standing would tell me I am—but Apple’s take on CALEA strikes me as a compelling argument.