The first problem is perhaps the less foreceful. The power to impeach specifically refer to crimes and misdemeanors and, prior to the current case, all cases involving the impeachment of president involved criminal charges. You might find this to be a less interesting point, but it's absolutely fair to point out that Democrats have set a new precedent and there is always some danger in setting new precedents.
You may want to check your facts. "Abuse of Power" was article of impeachment for both of the last 2 Impeachment cases being pursued (Clinton and Nixon). "High crimes and misdemeanors" is a phrase with a long history, from long before US even existed, and it does not mean "crimes under US law code".
Here is just one link talking about this.
The second problem in my opinion is far more serious. I will concede right away that you can absolutely have legitimate misgivings about how much Donald Trump can be trusted with executive authority in the comming years. However, what do you think would happen if you gave a list of hypothetical scenarios to strangers and asked them whether or not they constituted either "obstruction of congress" or "abuse of power"? I think you would get a lot of very different answers. I am not saying that the social norm, the ethical standard you wish to enforce here has no merit. What I am saying is that the grey area around the line you're trying to draw is too easy to manipulate. If Donald Trump committed purjury, we would be having a very different conversation: it's a clear line and the dispute would center around facts, not around how far the president is allowed to go. And that is the problem. People who dislike the president will say that he clearly crossed a line and people who like him will say that the line must be further because others before him did far worse.
If you lived in a world where Democrats and Republicans agreed on a strict limit to executive powers and observed high standards of moral behavior, I would completely agree with you: that was going too far. But in the current context, going after Trump for anything short of something really horrible is going to be perceived as highly partisan. To Republican voters and even to many moderates, the whole process looks like Democrats trying to circumvent the electoral process.
There is nothing grey about this. To use your example, I am quite sure if I gave these hypothetical scenarios to strangers and asked them whether or not they constituted either "obstruction of congress" or "abuse of power", most would agree that the first one is much LESS of an impeachable offense than others:
(1) President X lied to Congress, under oath, about sexual relations
(2) President X extorted our ally fighting a war with Russia for a public announcement to smear his political rival
(3) President X actively obstructed justice by refusing to provide any witnesses or documents to Congress (charged with oversight powers) for #2 and went on to publicly attack witnesses that DID come forward.
Do you honestly think our Founders or most people in US would put (1) as more of a problem for our President than (2) and (3)? I am sorry if you do.
Can you honestly say you're going to make America a better place by going after Donald Trump with procedural tricks? As far as I can tell, Democrats are throwing a hail marry, hoping they can get rid of him and face a less potent player comes 2020.
I honestly do not know whether it would be harder for a Dem to beat Trump or some other Republican that may come in his place. But I think that is irrelevant here.
I personally think Democrats should have had a lot more articles of impeachment against Trump, including a ton of violations of emolument clause (both foreign and domestic ones), campaign finance violations, obstruction of justice in Russia probe (Mueller had all the elements for it in at least 5 instances), and bribery (which Ukraine scandal qualifies for). In fact, I think the only reasons these are not included is because Dems were afraid of exactly the "procedural tricks" that would follow some of these and just making the case much longer and more "confusing" to people because it would get more drawn out.
Trump is the most corrupt President we've had who does not even try to hide it; so NOT impeaching him would set a very bad precedent for the future IMO.
Further, Trump and Republicans are actively not just inviting foreign interference in 2020 but also refuse to protect our voting infrastructure from such interference (Moscow Mitch tabled all the measures House attempted to pass). So another benefit of Impeachment might be a better chance to protect us against such interference in 2020.
