During the Roman Republic any official with a government position was immune to lawsuits. Once they were out of office they could (and would often be) charged with any variety of crimes (like bribery and corruption) by their political opponents. That is why Consuls made sure they had appointments to a governorship before they left office. Cicero was exiled from Rome for a while because his opponents took advantage of his not having an official position after he left office.

(Book – Cicero – Anthony Everitt)