A year after President Joe Biden's inauguration, more than two-thirds of Republican voters believe his election was illegitimate. The idea that the 2020 election was stolen from Donald Trump is now a defining issue of the Republican Party. Yet the story of how lies about election fraud made their way to the center of American politics has not been entirely told. In a new investigative collaboration, FRONTLINE and ProPublica trace the hidden sources of disinformation about the 2020 election, demonstrating how a handful of people have had an outsized impact on the current U.S. crisis of democratic legitimacy.