As we check our phones and watch the news, invariably a mention of former President Donald Trump's ongoing impeachment trial in the Unites States Senate is made. I know many people who loath Trump as well as many who love him - but that is not the issue to be addressed here. The real question that exists in my mind is why would Congress attempt to impeach a former president and why would the senate try that impeachment when the Constitutional and common law purpose of impeachment is not served by the process.
Impeachment is the subject of several other provisions of the Constitution. Article I, § 2, cl. 5, gives to the House of Representatives “the sole power of impeachment.” Article I, § 3, cl. 6, gives to the Senate “the sole power to try all impeachments,” requires that Senators be under oath or affirmation when sitting for that purpose, stipulates that the Chief Justice of the United States is to preside when the President of the United States is tried, and provides for conviction on the vote of two-thirds of the members present. Article I, § 3, cl. 7, limits the judgment after impeachment to removal from office and disqualification from future federal office and nothing prohibits an actual criminal trial of a former president.
Article 2 Section 4 of the Constitution clearly provides for who may be impeached:
The President, Vice President and all Civil Officers of the United States, shall be removed from Office on Impeachment for and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.
We can legally conclude that since the Chief Justice of the Supreme Court of the United States is not presiding over the trial in the Senate, that Donald Trump is not being considered the "President of the United States" in this trial - although he was clearly impeached on January 12, 2021, nine days before the end of his tenure. As such, the issue becomes whether or not the Senate has jurisdiction to try the case.
The timing of the trial has caused procedural due process issues which preempt any consideration of the facts and limit any legal remedy for criminal conduct by now Mr. Trump (whether or not it happened during his term as President) to the Judicial System. Simply stated, the main objective of impeachment is to remove a corrupt President, Vice President and/or Civil Officer from office - none of which describes the former president. As such, it is only proper that any alleged criminal conduct by a former president should be left to the purview of the any of the various U.S. Attorneys whose recent political patronage appointments certainly justify their most immediate attention to the matter.
With regard to "why" would jurisdiction be assumed over a proceeding without constitutional authority, one need only look at possible ulterior motives which seem to only be two-fold:
1) an impeachment conviction can result in an additional punishment that one can not hold future public federal office (which a criminal conviction doesn't necessarily accomplish); and,
2) an impeachment only requires a 2/3 vote; whereas a criminal conviction requires a unanimous verdict.
Again, the actions or inactions of the former president are of no consequence to the conversation. The fact is, there is a valid legal argument to be made that the current proceedings are unconstitutional; however, the Courts have been reluctant to get involved in impeachment matters over the years - classifying them as political matters outside their purview.