HK and Singapore have not declared martial law, per se. Nor Germany.
In this day and age, I'll predict whatever president declares marital law would be voted out of office or impeached. Democrat or Republican. It will be crossing the Rubicon, so to speak.
State of Emergency is not Martial Law.
Though they vary little in function, the nomenclature is different.
It is not necessary to declare martial law in order to have effective quarantines.
All you need to do is allow states to set up their own local quarantines in selected areas or around their states, including giving them permission to close their airports.
Martial law is like swatting a flea with a hammer—total overkill.