What will they do if the EU says they have to show proof of vaccination before they can enter any EU country?
Again, there won't be enough of those people to sway the politicians.
Or if their airline at MIA said they need to show such proof before getting a boarding pass?
That may happen for some international flights, it will NEVER be required for domestic flights (the White House has ruled out domestic vaccine passports). Remember, a majority of Americans don't have passports. Of those that do, how many are just taking an occasional trip every few years?
Just saw a video this morning from a former AA exec. Said that not only will vaccine certificates be likely required, like the old yellow books, they are likely to be required for a few years, even if the EU and the US get high percentage of their populations immunized.
What was the context those remarks were made in? If he's talking about international travel, they probably will. Domestically, it'll never happen.