Here's what happened to the Roman Republic ...
“… nor had they [the Romans] any more enemies whom there was ground to fear. This sense of security and this weakness on the part of their enemies caused the Roman people in appointing to the consulate to consider not a man's virtue, but his popularity. This drew to the office men who knew better how to get around men, not those who knew better how to conquer enemies. They then turned from those who had more popularity and gave it to those who had more power. Thus owing to the defectiveness of the institution it came about that good men were wholly excluded from consular rank." - N. Machiavelli
BTW - A consul was like a co-President (there were always two).