Mandates are essentially decrees by the executive branch of government.
The executive branch can legally rule by decree during Martial Law, but that is only allowed when civilian agencies are unable to maintain order.
The effects of the pandemic have not caused a break-down in civilian agencies/order.
Currently there is no justification for rule by mandates.
Mandates are orders from the government. We commonly get “orders” from governments. Typically they are in the form of laws and regulations--traffic laws, criminal laws, tax laws, civil rights laws, etc. The government has defined authority and processes for creating laws. That is not so true for mandates. The concern for the legality of mandates has recently arisen because of mandates, issued by the federal government that require people to be vaccinated against Covid 19 or to wear masks.
Are the vaccine and mask mandates legal? I say “no”. I’ll also say that, under extreme conditions the answer would be “yes”. Our laws do allow government to impose Martial Law. Under Martial law government authorities are given the power to make decrees that have the force of law. Enforcement of these decrees are not restrained by constitutional rights. Martial Law can be legally imposed when things have become so chaotic that civilian agencies are unable to maintain order. This can occur in war zones, after natural disasters, civil insurrections, etc. Is a pandemic justification for Martial Law? Per our laws the answer is yes if the Pandemic is so terrible that, as a result, our civilian agencies can no longer maintain control. Perhaps things got that bad when the Black Death ran through Europe. However, the Covid 19 pandemic has clearly not caused any breakdown in civil agencies. Our civil governments are working. There is no need for Martial Law. Given this there is no legal basis for government leaders to rule by decree—i.e. by issuing mandates. If mandatory vaccinations and mask-wearing are needed then the legislative bodies can pass laws that require these actions. Note, the courts may find even those laws unconstitutional. But, nevertheless, that is the way to regulate vaccinations and masking if it is to be required. The president, except during Martial Law, does not have the authority to decree mandates.