I dont know about the other countries, only about Venezuela. Back in the day, when Chavez became president the country was relatively in bad shape, Chavez was the head of the attempted coup and because of the country conditions he got popular. When he got in the government he seized control over the other public organs (among those the institution charged with the voting) by either firing and replacing or corrupting the people working there (the relevant one). The people with minor jobs get threatened with...well...their jobs. Massive firings happened some years ago because they unveiled a list of people who voted to make a referendum to make him resign.


Nothenless there is a way.