I’m not sure they could have picked two weaker offenses than what they did. Honestly, I think Obstruction of Congress is a non-starter if you support the concept of co-equal branches of government and separation of powers. If allowed to stand, that would set the precedent for future administrations that they have to do what Congress demands or be impeached. I don’t want an imperial presidency, but I certainly don’t want an imperial clown car, either.
If that was their best case, I think they came up short.
I don't think the issue is that the POTUS has to "do what Congress demands" as much as it's about the POTUS impeding Congress' investigative powers as a check on the presidency from the standpoint of them being a co-equal branch of government. In forbidding anyone from his Cabinet from testifying under oath before congressional committee(s) while publicly declaring his innocence while simultaneously declaring the impeachment process currently underway as a farce, a hoax, trumped up charges made by angry Democrats, Pres. Trump has effectively placed himself outside the law. That cannot be allowed to stand. Our Founding Fathers knew it. You know it. You simply refuse to acknowledge the inherent danger Pres. Trump's actions. This is more than him exerting Executive Privilege for information that he and he alone may possess. This is a sitting POTUS telling anyone under his direct control NOT to participate in a legal inquiry into his wrong-doing knowing full well that denying Congress access to eyewitnesses to his actions could very well provide Congress and the public greater insight into what he was doing and why concerning Ukraine.
From Federalist Paper 65:
A well-constituted court for the trial of impeachments is an object not more to be desired than difficult to be obtained in a government wholly elective. The subjects of its jurisdiction are those offenses which proceed from the misconduct of public men, or, in other words, from the abuse or violation of some public trust.
So, what did Pres. Trump do?
1) He used his position of power as POTUS to coerce the leader of another country (Ukraine) to re-open and investigation he readily knew involved an American citizen.
2) He knew that in publicly announcing that the investigation into Burima was re-opening said investigation it would have a negative impact on a political rival (former VP Joe Biden) in the "court of public opinion".
So, what does this have to do with violating the public trust? EVERYTHING!!
From the very beginning, Trump has stated publicly that our election process is rigged. Now, Republican politicians and voters are so very willing to stand idly by and allow him to effectively "rig" the upcoming 2020 presidential election by throwing up a false PR roadblock against a political rival. Look at what has already happened to Joe Biden in Iowa just recently?
You can't tell me that people aren't already buying into the false allegation. How long before this falsehood begins to permeate into the public sphere before it becomes the only thing voters will be talking about and Joe Biden has to defend on a frequent basis?
I know that Joe Biden isn't the only candidate on the Democrat ticket and that there's plenty of time before the public (and delegates) determines who the Democratic nominee will be, but right now according to polling data, Joe Biden is the front-runner and continues to be. How long before a false narrative brings him down - a narrative the current sitting POTUS helped spearhead by seeking aid from a foreign government? That's the issue so many of those on the Right completely ignore. And yet "legally voting" is suppose to be so precious to the GOP with all your redistricting, redlining, allegations of voter fraud, etc., etc., etc. You're so willing to overlook an issue that as a constitutional right and value YOU claim to be so sacred that you'd overlook your party leaders' misdeed just to save face.