Where do these messages appear? For example:

• In your email inbox (they are email messages)
• On web pages as advertising
• In search results when you run web searches
• As pop-up windows
• As desktop notifications
• Somewhere else

Also, is this problem on your Mac, or is it on an iOS device (iPhone or iPad)?

It happened on my desktop MAC mini: an email from the RNC. It was a political message evidently from the Republican National Committee, NOT a personal message. I have never had anything to do with the RNC! I think I deleted the message, but it is now nowhere in my Spam or Trash folders! Anyone know how this can happen?

I think we're all on a lot of lists. I'm sure you get other bulk mail, although much of it is filtered before you see it. Whether it was a list shared with or without permission, or someone you know gave them your address, this kind of thing happens.