Final answer:
A president who fills a vacated position can be elected for one additional full term if they have already served more than two years of their predecessor's term, but could potentially be eligible for two full terms if they serve up to two years of that term.
Step-by-step explanation:
The president can serve up to one year of the vacated term. According to the 22nd Amendment, a person who has served more than two years of a term to which someone else was elected cannot be elected more than once. This means that if a president is filling a vacated position and serves more than two years of that term, they can only be elected president once.
The 22nd Amendment to the United States Constitution sets the limits on the terms an individual can serve as president. Specifically, a president can be elected to office twice for a total of eight years. However, if a vice president or other successor fills a vacated presidency position and serves more than two years of the predecessor's term, they may only be elected to a single full term as president thereafter. So, if they serve up to two years of the previous president's term, they can potentially be elected for two additional full four-year terms; if they serve more than two years, they can only be elected for one more full term.