Subject: Re: On July 1 We Lost the Republic
Isn't one of the president's constitutional powers - and in fact a mandatory duty - to protect the U.S. from threats both foreign and domestic? If so, why can't Biden (or any other POTUS) simply claim that as the reason for assassinating (or jailing) anyone, including a former - and potentially future - threat to America?

Nope. The President's Constitutional powers are listed in Article II, which is linked below:

https://constitution.congress....

He doesn't have a roving portfolio to kill anyone he claims is a threat to the U.S.