The best way to prove voter fraud exists
... is to commit some.

Hired a for-profit firm to register
voters, for which the firm

• In 2004 threw away registration forms
  of people who selected "Democrat.")
   
• In 2012 was paid $3 million by the
  Republican National Committee and
  subsequently caught red handed
  in Florida and other states,
  having registered as Republican
  ... dead people, people living at
  gas stations, sharing the same
  signature, etc.