(Bloomberg) -- Zalmay Khalilzad, the U.S. envoy who has frequently served as America’s liaison to Afghan leaders since the September 2001 terrorist attacks, is stepping down, Secretary of State Antony Blinken said. 

Khalilzad, who had positions in the administrations of Ronald Reagan, George W. Bush and Donald Trump before President Joe Biden’s election, will be replaced by his deputy, Thomas West, Blinken said in a statement Monday. 

“As Special Representative for Afghan Reconciliation Zalmay Khalilzad steps down from his role, I extend my gratitude for his decades of service to the American people,” Blinken said in his statement. 

Khalilzad, 70, was born and raised in Afghanistan but eventually moved to the U.S., where he received a doctorate at the University of Chicago. After entering government service in the 1980s, he was increasingly relied on for his expertise on a nation that has often been near the heart of U.S. foreign policy, first as a Cold War battlefield after Russia’s invasion and then as priority for the Bush administration as it sought to oust the Taliban regime hosting al-Qaeda leader Osama bin Laden. 

Afghanistan was hardly Khalilzad’s only remit. He also served as America’s ambassador to Iraq starting in 2005 and became UN ambassador in 2007. After the start of the Obama administration, Khalilzad started an advisory firm and served in a leadership role for a number of Washington think tanks. 

Under the Trump administration, Khalilzad was tasked with brokering talks with the Taliban in Qatar that eventually led to a 2020 peace deal that Biden inherited, calling for the removal of all U.S. troops. 

Khalilzad’s departure from government service means he will be freer to discuss the events behind that 2020 agreement, and the subsequent failure by the U.S. to predict the Taliban’s swift return to power, forcing a harried American withdrawal in August.  He made clear he intends to do so.

“The political arrangement between the Afghan government and the Taliban did not go forward as envisaged,” Khalilzad wrote in a resignation letter to Blinken. “The reasons for this are too complex, and I will share my thoughts in the coming days and weeks, after leaving government service.”

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