Got it, but I think most democracies (for example US, Brazil, Argentina) have a line of succession either in their constitution or in the amendments that follow

Got it, but I think most democracies (for example US, Brazil, Argentina) have a line of succession either in their constitution or in the amendments that follow it. Whenever anyone takes the role of president next, they have full authority, power, and responsibilities of a president, even if in some cases they don't have the title of President. I know of a few examples that it's required to have new elections months after a president step down, which is the case of India, but even then the acting president has the full power of a president.