They just don’t get it – The First: Quid Pro Quo. The issue isn’t “quid pro quo” (QPQ) per se. QPQ’s happen all the time in statesmanship. We’ll give you foreign aid if you … The real issue is using your office for personal political gain — doing a quid pro quo that explicitly involves investigating your political opponent (personal gain), and using for leverage money explicitly authorized by Congress (abuse of authority). It’s the personal gain that makes this an abuse of power.
They just don’t get it – The Second: Rules of Evidence and Testimony. For all the blathering of Trump about evidence and trials, he’s forgetting one thing: THIS ISN’T A TRIAL. If the House chooses to move forward articles of impeachment, there will be a trial. That will be in the Senate, presided over by the Chief Justice, under the rules defined by the Senate. It won’t be a criminal trial … which means that the 6th amendment doesn’t come into play, and the right to confront your accuser. Remember: With impeachment, the most severe penalty is not jail, it is removal from office.
But we’re not at an impeachment trial yet. Right now, what the House is doing is analogous to the police and prosecutors doing the investigation to determine if there is a case to be prosecuted. Grand juries. Investigative legwork. There might be tips from informants, but the informant may never be needed again if the investigation of the tip finds enough evidence. This is all gathering evidence.
If the house investigative team finds sufficient evidence, then it will present their case to the full House. If the full House agrees there is a case, they will vote and pass articles of impeachment. An indictment, so to speak. This doesn’t mean guilt. It means the House feels there is enough evidence for a trial.
At that point — and only that point — the Senate conducts a trial to prove or disprove those articles. If proven, the person is removed from office. The Constitution defines no rules for this trial, other than the Chief Justice presides. So it is for Congress to determine the rules … not traditional jury rules, because this isn’t a criminal trial.
Lastly, remember that the Constitution does not require there to be a crime, in a criminal sense. It is also up to Congress to determine what it believes are sufficient “high crimes and misdemeanors”. Often, it has been abuse of power, in the form of obstruction of justice. Basically, the Congress doesn’t like it when the President tries to go around Congress, not let Congress do its investigatory job, or ignore the will of Congress, who supposedly represent the people.
There’s a great discussion of this latter issue in the TrumpConLaw podcast: https://trumpconlaw.com/35-confrontation-clause