Sometimes current/former politicians are referred to by their most senior held (previous or current) title, rather than strictly their current title.
For example, in a 2016 Presidential debate, Hillary Clinton was referred to as 'secretary', even though her role of secretary of state ceased 3 years' prior in Feb 2013.
Another example is Barack Obama's current medium profile stating 'President'.
When does the convention of referring to a politician by their most senior held title (rather than strictly their current title only) apply? Is it a uniquely American thing, or is it standard practice in politics everywhere? It contrasts somewhat to some other professions like medicine or finance, where referring to oneself by a previous position can be viewed as inaccurate (e.g. as a doctor or financial planner respectively, if one does not currently hold the said position).