Seven senators on Tuesday urgently appealed to President Joe Biden to grant clemency to Leonard Peltier, the ailing 78-year-old Native American rights activist whom the U.S. government put in prison 46 years ago after a trial riddled with misconduct and racism.

“Mr. Peltier’s continued imprisonment defies the promises of justice, and the power to exercise mercy in this case lies solely within your discretion,” reads a letter to Biden from Democratic Sens. Brian Schatz (Hawaii), Patrick Leahy (Vt.), Elizabeth Warren (Mass.), Ed Markey (Mass.), Bernie Sanders (Vt.), Mazie Hirono (Hawaii) and Tina Smith (Minn.).

“Mr. Peltier has spent more than half of his life behind bars,” the senators said. “We commend the steps that your administration has taken to right past wrongs of our government’s treatment of Native Americans, particularly through [Interior] Secretary [Deb] Haaland’s leadership and her Federal Indian Boarding School Initiative. Furthermore, your administration has demonstrated a laudable commitment to upholding the core American values of liberty and justice, and rectifying inequities in the criminal justice system.”