"It stuns me that a member of Congress listened into that conversation"

If I'm remembering correctly, what I heard yesterday was that Trump's call came in as Mrs. Johnson was en route to the airport to receive the body of her husband. She put her phone 'on speaker' and Rep. Wilson could not help but hear what was said. Therefore, it's rather unfair to suggest that she listened in or behaved inappropriately.

What the president should have known is that although a call from any president is something of an honour, some moments are better than other. In fact, some moments would be entirely inappropriate.

Phoning someone you do not know (and even many that you do know) as they are about to receive the body of their beloved spouse or child isn't likely to be great timing. A more sensitive person would have known that.