On Sunday, President Donald Trump took aim at one of his favorite targets: Senator Elizabeth Warren, who is hoping to unseat him in 2020. Responding to a video Warren posted on Instagram in which she drinks a beer in her kitchen and introduces her husband, Trump tweeted:

“If Elizabeth Warren, often referred to by me as Pocahontas, did this commercial from Bighorn or Wounded Knee instead of her kitchen, with her husband dressed in full Indian garb, it would have been a smash!”

Trump has long attacked Warren for claiming Cherokee and Delaware ancestry, belittling her as “Pocahontas” and, more recently, challenging her to prove her claims using a DNA test. But his invocation of Wounded Knee—one of the most shameful episodes in U.S. history—is a new low.

On December 29, 1890, the U.S. 7th Cavalry massacred hundreds of Lakota near Wounded Knee Creek in South Dakota. It was hardly the largest settler massacre of Native peoples, but it is the most infamous. To Native peoples it has long been a symbol of U.S. brutality, a reminder of the immorality of a nation that claimed it was bringing civilization but instead brought a slaughter.