@blatham,
That was a fine legal philosophy for the time. But it was invalidated when the Democrats voted that it is OK for presidents to abuse their power and Bill Clinton should not be removed from office for having done so.
There's no going back on that precedent now.
That said, there is no evidence that Mr. Trump has abused his power. He could have wanted the Bidens investigated because he genuinely thought that they were up to no good in Ukraine.