Which of the following is NOT a former living president?

The choice indicating that Donald John Trump is not a former living president is correct because he is the most recent president, having served from January 2017 until January 2021. In contrast, Bill Clinton, George W. Bush, and Joseph Biden all hold the status of former presidents; they have completed their terms, with Biden currently serving as president. Therefore, it is consistent to identify Trump as the only individual on the list who is not a former president, as he is a current living president and has not yet completed a subsequent term that would qualify him as a former president. This contextual understanding clarifies the distinction among the individuals listed and highlights why Donald Trump does not fit the criteria outlined in the question.