If Trump really believes it is rigged, why would he run again?  

If Trump Truly believes the election is rigged, then by his own admission and logic, running again would result in him losing. 

He doesn't really believe that. His fragile ego would never allow him to be put into a position where he is sure to lose again, so of course, he knows it wasn't rigged, which is why he is talking about running again.

Trump knows he lost fair and square, so he wants to make another run for it in another "non-rigged" election.

Just saying he's going to run again is proof that he believes the system DOES work.

He's a fraud, plain and simple.