Genuine question: what upside does it have against supply chain attacks?
Is it possible that an adversary to implement a backdoor into a chip design, without Apple noticing it?
I'm not a chip designer so perhaps the answer is obvious to some of you guys, but I'd expect some verification mechanism at Apple's side of the manufactured chips to match their original design to verify that they aren't tampered with?
Zero upside, probably a downside.
Apple has a top notch logistics and security processes which had mitigated the issue of supply chain attack in China which his willing and capable of producing such attacks.
Moving some production to the USA might induce some sloppiness in this due a perceived inferior risk.
Also, some security measures requested by Apple to manufacturers in other countries are probably illegal in the USA.
The article doesn't mention supply chain attacks. What context are you referring to?
I'll take a guess and agree with TOMDM. It's about China invading or blockading Taiwan (remember the US attack/blockade against Cuba? Exactly that.) and thus denying America physical chip shipments.
Very much possible. Talking more generally about microelectronics - You can imagine the DoD is very interested in making sure they're not putting 'bad' chips in their military hardware, whether 'bad' means backdoored or merely counterfeit.
Manufacturing chips in the US means the DoD can investigate the acutal fabs and put cleared personnel on the manufacturing line to make sure nothing untoward is going on. Another strategy is to investigate the chip after it's been manufactured somewhere else and prove that it's the same chip you designed, but that's quite difficult.
If you're interested you can read up on the Trusted & Assured Microelectronics (T&AM) program.