As we’ve seen in the legal briefs leading up to this impeachment and now in the debate itself, precedents matter in these kinds of issues. The question whether a President could be impeached after his term was over hadn’t been answered by prior precedents. Hence it was a question now. The Senate just voted 56-44 affirming the constitutionality of Trump’s impeachment after he left office. That vote likely means he will not actually be convicted. But it also means that, if some future President decides to incite riots at the very end of his term, this precedent has established that he could still be impeached. If nothing else, the second Trump impeachment has at least accomplished that much.