The President told Trump to stop whining and to go work for his votes. Tim Steller provides ample evidence from local Arizona/Pima/Tucson sources that our election system and its supporting machinery are solid, reliable, and valid: Steller: Society may be rigged, but not election. And election officials across the nation from both political parties defend the validity of our elections, Officials Fight Donald Trump’s Claims of a Rigged Vote.
In other words, Trump and his defenders are spreading lies about the election for their own political purposes.
Read more about Trump's unhingement in the related post today, "Trump succumbs to ideological psychoses."
And Catherine Rampell in another post here today ("Can Democracy survive in a post-factual world?") offers an explanation for why so many of Trump's supporters are deaf to the facts about our elections.