Here's the latest from Josh Marshal:
It may not seem terribly important right now with all the stories roiling the campaign. But I think there's a good chance it's the most important. Over the last 48 hours Trump's allies, surrogates and now Trump himself have forcibly injected the topic of voter fraud or 'election rigging' into the election.
Vote fraud is clearly the aim in what is coming from Trump allies. But Trump's own comment - "I'm afraid the election's gonna be rigged, I have to be honest" - seems to suggest some broader effort to manufacture votes or falsify numbers, to allude to some broader conspiracy. Regardless, Trump is now pressing this issue to lay the groundwork to discredit and quite possibly resist the outcome of the November election.
It's true that Republicans have been very disingenuously pushing the 'voter fraud' con for years, especially as the power of minority voting has grown over the last two decades. However, as bad as that has been, there's a major difference. Republicans to date have almost always used bogus claims of 'voter fraud' to rev up their troops and build support for restrictive voting laws, largely focused on minority voters. A number of those laws have been overturned by federal courts in the last week. A notable case was North Carolina where the Court found that the changes were intentionally designed to limit voting by black North Carolinians.
What Republicans politicians have virtually never done was use this canard to lay the groundwork for rejecting the result of a national election. This is Donald Trump, not a normal politician. You should not be surprised if he refuses to accept the result of an electoral defeat or calls on his supporters to resist it.