Trump makes baseless claim that he won the popular vote excluding 'millions' of 'illegal voters' | Business Insider
As fact checking sites have explained, this claim seems to have originated with one guy, who provided no evidence whatsoever; it then got attention at Infowars and the idiot Gateway Pundit's site; and now, if you can believe him, Trump believes it too. Or, he is willing to use it if it suits his purposes.
I mean, seriously, what's worse? - a President who is dumb enough to be convinced by whatever appears on conspiracy sites; or a President so morally base in his "win at any cost" attitude that he will use conspiracy claims not caring if they are false, and knowing many of his followers will believe him, if they suit his purposes?
Update: Vox's commentary on this is worth reading, too.