In February, the YourNewsWire page on Facebook was at its peak popularity, boosted by its salacious post claiming that Justin Trudeau, the Canadian prime minister, was Fidel Castro's love child.

That story, shared 1,800 times, represented exactly the kind of content Facebook Inc. had promised to clean up on its site — and which YourNewsWire prolifically produced. It was created to drive attention, and therefore advertising revenue. It was also provably false.

YourNewsWire is still publishing. But its stories aren't going viral on Facebook anymore, and the website is finding it more difficult to make money. In the case of YourNewsWire, at least, Facebook has delivered on its promises in time for the U.S. midterm elections on Tuesday.