“You can argue that it wasn’t a crime,”
No you can't. There was no crime. There is no criminal charge. There is no arguing for and against those factual statements.
Further, the POTUS has an obligation to investigate corruption. And there is plenty of corruption to investigate - by the Bidens. Whether or not Biden is a candidate is a mute point. If evidence emerges of corruption (which it has - by Biden's own words, on camera), then it has to be investigated.