Donald Trump’s recent comments about the prospect of a rigged election and widespread voter fraud should he lose have taken his conspiracy theories to a new level.

Political conspiracies are nothing new, and date back millennia–the Roman Empire was rife with intrigue and plots--but Trump’s endorsement of conspiracies is unprecedented in American politics. No modern politician has so successfully and routinely employed conspiracy theories as Trump.

Trump has implicitly or explicitly endorsed several prominent conspiracy theories, including about the death of Supreme Court Justice Antonin Scalia. When asked about it during a media interview Trump responded, “I’m hearing it’s a big topic… They say they found a pillow on his face, which is a pretty unusual place to find a pillow.” (In fact Scalia died of natural causes, a pillow was not found over his face, and his family was aware he’d been ill for some time.)

Trump has also endorsed several explicitly anti-science conspiracy theories including that childhood vaccines cause autism, and that global warming is a hoax (tweeting on Nov. 6, 2012 that “The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive”). Trump’s best known conspiracy theory, however, involves questions about President Obama’s birthplace, which was of course a clear challenge to his legitimacy as president under the Constitution.

But recently Trump took a new tack. Vanity Fair noted last week that “Donald Trump is once again down in the polls, and like clockwork, the Republican nominee has resumed warning his supporters that ‘Crooked Hillary’ and her allies will steal the election. His latest theory as to how the vast left-wing conspiracy will cheat him out of the White House? Undocumented immigrants, Trump says, are receiving fast-tracked U.S. citizenship so they can vote for Hillary Clinton in November.”

Trump has trafficked in many conspiracy theories for years, but this is one is different. Here’s why.

By employing this specific type of conspiracy theory Trump sets up a no-lose situation for himself (and those who endorse him). Trump has called into question the legitimacy of the very foundation of a representative democracy: voting.

A conspiracy about the prospect of voter fraud in case of Trump’s loss resonates personally and emotionally with ordinary voters in a way that other conspiracies will not: Not everyone cares whether or not Obama was born in the United States, and even fewer likely care about the exact circumstances of Justice Scalia’s death. But voting is a different matter: it is the people’s voice and right, and everyone wants their voice heard. As US District Judge Mark Walker ruled recently, “No right is more precious than having a voice in our elections.”

Voter fraud is not unheard of in elections around the world, of course, and while some voter fraud is possible, rigging an entire American election would be virtually impossible as a practical matter. There are simply too many independent machines to alter all of them, and in any event even if Trump’s claim was true, there are not enough recently-minted citizen migrants to significantly alter voting patterns across the country.

The voter fraud conspiracy is especially insidious because it cannot be conclusively disproven. Any investigations that find no truth to the allegations can simply and easily be dismissed as whitewashes and cover-ups. The nature of conspiracy theory is such that any evidence that contradicts or undermines the theory is assumed to itself be part of that that cover up. In this way conspiracy theories are self-perpetuating and what in science is called non-falsifiable; that is, they cannot be proven wrong.

It’s not clear whether Trump himself genuinely believes that conspiracy–after all, if he is certain that the system is fatally rigged against him, why bother to continue?–or if it’s just one of his trademark bluffs and blusters. If Trump loses the election in November, there will be some people-perhaps thousands, perhaps millions-who harbor some doubt about the legitimacy of the outcome. And that can indeed undermine confidence in the country.