CartoDB embedding doesn’t work

1 The [iframe] custom shortcut

Turns out the content from CartoDB was being blocked by Privacy Badger a browser plugin that disables trackers and other malicious content. The solution was to allow content from username.cartodb.com as in the image below

Privacy badger screenshot

The Magic “Paste and it Just Works(tm)” Method

This apparently only works in the Visual Editor and only works for blogs hosted on WordPress.com, which was not the case for my site. Thanks to Tom Malone for pointing this out in the comments above.