The American Bar Association (ABA) has canceled a lecture by former South African President F.W. de Klerk, who shared the 1993 Nobel Peace Prize with Nelson Mandela, because of his role in the former apartheid regime.

De Klerk helped South Africa make the transition to multi-racial democracy, freeing Mandela from prison and legalizing the African National Congress (ANC). He served as deputy president to Mandela in the first post-apartheid government.

Since then, de Klerk has been recognized around the world as an expert in conflict resolution and negotiation. He was to have addressed the ABA on the topic of “rule of law, constitutional democracy, minority rights, social change, racism and global security,” according to South African news website News24.com.

However, the ABA canceled the lecture after protests. The objections cited the murders of the “Cradock Four,” political activists who were killed by the apartheid regime in 1985.

The case was considered by South Africa’s Truth and Reconciliation Commission in the 1990s, which denied amnesty to six of the seven security policemen involved in the assassinations. However, activists now claim that de Klerk, who was then a member of the Cabinet, was among the government ministers who knew of the assassinations.

In 2009, de Klerk hailed the election of U.S. President Barack Obama as “a powerful message not only for America and the world, but for us in Africa.”

The ABA has been criticized for decades for behaving as a “left-wing advocacy group,” especially during judicial confirmations.

Joel B. Pollak is Senior Editor-at-Large at Breitbart News and the host of Breitbart News Sunday on Sirius XM Patriot on Sunday evenings from 7 p.m. to 10 p.m. ET (4 p.m. to 7 p.m. PT). His new book, RED NOVEMBER, is available for pre-order. He is a winner of the 2018 Robert Novak Journalism Alumni Fellowship. Follow him on Twitter at @joelpollak.