The US political system is now so deeply divided along partisan lines that it's increasingly difficult to imagine what "an impeachable offense" would look like. Impeachment requires that many members of Congress are willing to go against a President of their own party, and that doesn't really happen any more, at least not at the scale needed for impeachment.

The founders seem to have imagined that Congress (as a whole) would have an adversarial relationship with the President. But they failed to foresee the levels of partisanship we have today which have resulted in ~half of Congress being very closely allied with the President.

When the US was less divided, things like ethics or morals or even just not openly breaking the law mattered a lot more. Now, people (at least, the people who vote the most) care more about "is my party in power", and either don't know about or disregard everything else. I include "don't know" because if all you listen to is Fox news and social networks feeding you ideas that you already agree with then you can easily be completely unaware of things like this.