maria silvaniax

What proof?
Perhaps I’m not understanding your last post, “Just try to apply for a U.S. Passport?” the OP’s SO US citizen, has not obtained the CRBA, 'Proof of US citizenship' with out the certificate no US passport can be issued to the applicant.

You can get a U.S. passport without a CRBA.
Proof of the child's U.S. citizenship (the same proof submitted for the CRBA): Proof of father's U.S. citizenship + Proof that father has been present in the U.S. for 5 years, including 2 after the age of 14 + Proof that this is the child's father + The father's acknowledgement of paternity
You have not given any reason why the passport application will be "denied".

I was seeing your post as a stand-alone comment, “Just try to apply for a U.S. Passport?” Absolutely can file for the CRBA and US passport at the same time, if this is what you meant.
If the CRBA is denied the passport fee will be returned and passport application denied at that time.

Of course they have proof of U.S. citizenship. (Otherwise how would they apply for the CRBA?) They just don't have the father there.

Exactly. Your situation is not the same. You were telling the OP to just list their child on the I-129F and apply for a K-2 visa for them. That is not the correct thing for the OP to do. They need the CRBA and then get a US passport for the child. You are confusing the situation for the OP with your own situation, which is not equal to that of the OP and the topic of this thread.

If the child is a USC because one of the parents is, then they do not need a K2 visa. The child needs to get a US passport, not a US visa.

Incorrect, a K2 visa will not be issued to the baby because the baby has a US Citizen parent. They would be told to obtain a CRBA
Disregard it, it was incorrect.