Originally Posted by Often1

Yes.

Although looking at this as what an air carrier does or does not want is the wrong way to look at it. Air carriers would much prefer that there were no travel document requirements or, perhaps more particularly, that it was not their responsibility to check them.

Air carriers can be fined significant amounts of money for permitting a person to board without proper documents. While they may try to collect that from the passenger, pursuing many people for $10K or thereabouts can be fruitless. Thus, they train their people to require the documents and be done with it. As an institutional matter, carriers would far prefer to lose one passenger's business to paying a significant fine. This is not to suggest that CBP would impose such a fine here.

But, there is an option. Any US consulate can issue a temporary passport (passport replacing document) which is good for the dates and route of travel back to the US. That is why the best advice if you lose your passport, have it stolen or screw up and let it expire, is to head to the consulate, not the airport. The land border is fine if you are in Canada, but suffers from the same or a greater problem if you are heading to the US from other than Canada.