From The Intercept:

By targeting essential security keys used to encrypt data stored on Apple’s devices, the researchers have sought to thwart the company’s attempts to provide mobile security to hundreds of millions of Apple customers across the globe. Studying both “physical” and “non-invasive” techniques, U.S. government-sponsored research has been aimed at discovering ways to decrypt and ultimately penetrate Apple’s encrypted firmware. This could enable spies to plant malicious code on Apple devices and seek out potential vulnerabilities in other parts of the iPhone and iPad currently masked by encryption.

Very disappointing to see this happen, but glad to see Cook stand firm to the extent he can. Ultimately the problem with any backdoor is that if it works for one person than others can exploit it. There is not some kind of middle ground where we can know for certain our devices are secure but also that the government can snoop on them. We deserve secure systems, and our privacy. These things were embedded in our fourth amendment and I think the interest of law enforcement in snooping on our communications should not override it.