Keep in mind that the founders were considering a scenario in which there was no 22nd Amendment limiting presidents to two terms. The Framers had to worry about a president who might abuse power to hold on to office not just once, but multiple times. Without term limits, it was even more important to deter presidents from using their vast powers to stay in office for long periods of time. That meant election shenanigans had to be punished. Given the short period between the election and inauguration, especially in the 18th century, and even before inauguration was moved from March 4 to January 20, that suggests the framers envisioned trials that might spill beyond the impeached president’s term. England’s impeachment of Hastings, for example, took seven years.
A fair reading of the convention debate indicates that the framers supported a broad impeachment process for presidential misconduct at the end of their terms, especially with respect to re-election abuses, corrupting or contesting electors, and insurrections. Together with their respect for the English tradition of impeachments of officials who had left their offices, that suggests Rep. Raskin was correct in arguing against the idea of a “January exception.”
This is a classic case where a close reading of the Constitution is only the beginning of interpretation, not the end. Given the lack of clarity of the text itself, we look to the writings of the framers to clarify the purposes of the clause — which lines up with common sense: The original meaning of the impeachment clauses is that they applied to ex-presidents, as well as presidents.