The largest tribal advocacy group in the United States condemned President Trump on Monday for his late-night tweets about Sen. Elizabeth Warren in which he called her “Pocahontas” and invoked the Wounded Knee Massacre.

“We condemn in the strongest possible terms the casual and callous use of these events as part of a political attack. Hundreds of Lakota, Cheyenne, and Arapaho people lost their lives at the hands of the invading U.S. Army during these events, and their memories should not be desecrated as a rhetorical punch line,” said National Congress of American Indians President Jefferson Keel in a statement.