So someone doesn't have to supply documents proving citizenship as part of the passport application process?
Logically speaking if a passport is the only document that proves citizenship, then the other side of that coin is that no other documents proves citizenship. So if a passport is the only document to prove citizenship and you need a document that proves citizenship to get a password then the only document you can submit to get a passport is a passport.
Or...
Other documents that prove citizenship exist and are submitted as part of the passport application process.
WW
(Don't get me wrong a passport is a great way to prove citizenship. Can make life a lot easier. My wife and I just completed Global Entry (the international version of TSA Precheck, and the process was easy since we both had passports.)