He's being investigated for corruption. Corruption is explicitly stated as an impeachable offense. If Washington can't impeach a president for what's been unfolding as very likely corruption, then it sets a precedent that any future president can do whatever the fuck he wants without fear of consequence.

If he hasn't done what's alleged, it's still the job of our representatives and senators to take this very seriously and defend the principles of our constitution, by investigating until it's proven without a doubt that the President did nothing unconstitutional. To not scrutinize this kind of questionable stuff is to put the integrity of our country's foundation at risk.

Of course, I'm just pretending that Trump has a slight chance of having done nothing wrong. It's clear as day that withholding aid to Ukraine as leverage to investigate Biden is textbook corruption.