That would be Nancy McLean's attack on James Buchanan. Now Phil Magness has posted a spreadsheet of her errors. Between this and "The Sound of Silence. A Review Essay of Nancy Maclean's Democracy in Chains: The Deep History of the Radical Right's Stealth Plan for America" forthcoming in the Journal of Economic Literature, you'd think her reputation as a historian would take a huge, lasting hit.
But since the Left seems to be invested in her story, that remains to be seen.