It’s not so much that when the president does it it is not a crime as it is that the only remedy when the president does it is impeachment.
And if the president does it and gets away with it and thumb’s his nose at the plain language of the Constitution, then that normalizes it and, in a sense, legalizes it.
This was my concern about giving Bush a pass on torture.
Trump’s crimes so far are more pedestrian but still insidious.