Republican presidential nominee Donald Trump, behind in the polls, has started claiming that the election will be stolen from him because it is “rigged.” When Trump talks about the election being stolen from him, he seems to be referring to a range of issues, from voter fraud to the media being allied against him. He also said this week that he expects more than a million “deceased individuals” to vote against him.

These claims have the potential to resonate with many Americans who already question the integrity of this country’s elections. A September Washington Post-ABC News poll found that 46 percent of registered voters believe that electoral fraud happens at least somewhat often.

But stealing an election in this country isn’t easy. In fact, experts say it’s nearly impossible given how voting works. And documented instances of voter fraud are actually very rare. Wendy R. Weiser, director of the Democracy Program at the Brennan Center for Justice, said the rate of fraud is smaller than the rate of Americans being struck by lightning.