Donald Trump, a man who prizes winning above all, shows no interest in being an agreeable loser, should it come to that. The Republican U.S. presidential nominee complains about a "rigged" system favoring Democrat Hillary Clinton and says he will lose in Pennsylvania, a battleground state, only "if cheating goes on."

The fact that Clinton has opened a commanding lead in polls of Pennsylvania voters hasn't squelched talks of a fixed election, since Trump and many of his supporters suggest that polls, too, are rigged against him. Even though the U.S. supplies advisers and observers to monitor democratic elections around the globe, Trump is far from the first politician to question the integrity and fairness of America's own voting. He may, however, be the first presidential candidate to suggest before Election Day that the results could be dishonest.

1. What does Trump say might happen?

He's urging supporters, at least in Pennsylvania, to monitor polling stations to "make sure other people don't come in and vote five times." Republican strategist Roger Stone, a Trump supporter, has suggested that since voting machines "are essentially a computer," they can be programmed to give false results.

2. Why is Trump singling out Pennsylvania?

It's one of 17 states that won't require voters to show some form of identification. Plus, there's some history. Conspiracy theories shared on the Internet held that fraud had cost Republican Mitt Romney votes in sections of Philadelphia in the 2012 election. (Those theories were debunked.) On Election Day in 2008, two members of the New Black Panther Party, wearing military gear, stood outside a Philadelphia polling place, prompting a federal voter-intimidation lawsuit against the men and their black nationalist organization. Republicans howled when the Justice Department dismissed most of the case.

3. Why won't Pennsylvania voters have to show photo IDs?

Photo-ID requirements for voters are a recent innovation, part of a surge in new voting restrictions passed by state governments controlled by Republicans after the Supreme Court stripped the federal government of the right to block them preemptively. Eight states have strict photo-ID requirements. Pennsylvania passed one, but a state judge struck it down in 2014.

4. What's the argument against requiring photo IDs?

Not everybody has a driver's license, passport or other photo ID, and acquiring one can take effort or money. That's why critics say photo-ID requirements have a disproportionate impact on blacks and Hispanics, the elderly, students and people with disabilities. The judge who overturned Pennsylvania's photo-ID law wrote that it would "disenfranchise hundreds of thousands of valid voters." Photo IDs are required of voters in some other countries, but they're also easier to get.

5. How big a problem is voter fraud?

It's far from impossible to cast an illegal vote but a great deal more difficult to do so on a scale that decides an election. For every study suggesting widespread voting by ineligible non-citizens, felons or dead people, there are multiple studies or investigations painting voter fraud as rare and inconsequential.

6. Is voter fraud the only concern?

Not even close. From hanging chads to broken-down machines, the highly decentralized, volunteer-dependent U.S. voting system produces gripes and laments every election. A decade ago, following back-to-back wins by George W. Bush, it was Democrats who questioned the reliability and integrity of electronic voting machines like those made by industry leader Diebold Inc., which had an active Bush supporter as its chief executive. The Republican National Committee remains under court supervision because of a 1981 "National Ballot Security Task Force" initiative in New Jersey that was found to have been an effort to intimidate minority voters.