To use the language of civil trials, House Democrats have brought a complaint to the Senate that President Donald Trump deserves removal from office and Trump's lawyers have countered that the complaint fails to state a claim and so must be dismissed.
Trump's lawyers have the better argument.
The Democratic complaint — articles of impeachment for abuse of power and obstruction of justice — makes only an ad hominem argument. Such an accusation that a person inherently lacks credibility proves nothing. It only defames. It is a pseudo-argument masquerading as a revelation of truth.
Every ad hominem attack is a logical failure. Attacking the person does not address the truth or falsity of his or her narrative. Ad hominem attacks seek to persuade through inference: We are to infer that a bad person can't or won't tell the truth.
The form of an ad hominem accusation is this: You are a bad person; you have bad motives; therefore, nothing you say is right. We hear a lot of those arguments these days.
But a good person can lie and a bad person can tell the truth.
The sum and substance of the Democrats' articles of impeachment are that Donald Trump is: 1) a "dictator" (Rep. Jerry Nadler); or 2) a "danger to our forthcoming presidential election" (Rep. Adam Schiff).
These accusations demean Trump's character, no more than that. They do not disprove his version of events.