“They can be more concerned about their election, or their legacies. And I would argue to many of them: your legacy is more important than the next election.’”
Legacy as used here and in similar statements means legacy in the eyes of the elite: the New York Times, the liberal establishment and liberal historians.
Obviously it’s not “legacy” in the eyes of the actual voters you were supposed to represent, because they are the ones you have to oppose in the name of your “legacy”.
Most of these politicians will be forgotten very quickly once they leave office ... some while they're still in office!