The entire thread is based on a false premise. The requirement of a negative test within 72 hours of departure is made by the Portuguese government, not the carrier.

Please note that, as per the directive of the Portuguese Government (Decree Law no. 7595-A / 2020, of July 31), all passengers (including Portuguese citizens, residing in Portugal and their families) on the flights described in paragraphs c) and d) must present proof of laboratory testing (RT-PCR) for the screening of SARS-CoV-2, with a negative result, performed within 72 hours prior to the time of departure, or they will be denied boarding.

This appears not only on the carrier website, but is repeated in TIMATIC in similar language.

1. OP will be denied boarding.
2. He will have no recourse.

Be careful of the test you select in the US. Rapid antigen tests are available for private use, but they are not PCR tests and apparently Portugal does not accept them.