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(CNN) —  

Former US special envoy for Ukraine Kurt Volker, who has become a key player in House Democrats’ impeachment inquiry into President Donald Trump, announced Monday he is stepping down as executive director of Arizona State University’s McCain Institute.

“Today, I informed ASU President (Michael) Crow and Mrs. (Cindy) McCain that I believe the recent media focus on my work as U.S. Special Representative for Ukraine Negotiations risks becoming a distraction from the accomplishments and continued growth of the Institute, and therefore I am stepping down as Executive Director of the McCain Institute for International Leadership,” Volker said in a statement.

Volker is one of the people at the center of the House’s impeachment inquiry examining Trump’s July 25 phone call with Ukrainian President Volodymyr Zelensky, in which Trump pressured Ukraine to investigate former Vice President Joe Biden and his son, Hunter. CNN previously reported that Zelensky had joked with Volker about Rudy Giuliani, Trump’s personal attorney who is also a key player in the scandal, before the phone call was made.

Volker later set up a meeting between Giuliani, who had been interested in getting Ukraine to investigate Joe and Hunter Biden, and a Zelensky adviser in an effort to get the Biden matter out of official talks.

There is no evidence of wrongdoing by either Joe or Hunter Biden.

Last week, Volker testified before three congressional committees – making him the first official to testify on the whistleblower complaint that contains allegations about Trump’s actions. He had held onto his post in the administration until late last month, when he resigned one day after the White House made the complaint – which named him – public.

Amid rumors that he was planning to step down, Volker told staff at the institute last week that he had no imminent plans to resign. The former diplomat wanted to keep doing his job, one of the sources who was in the meeting told CNN at the time, but Volker also recognized he might have to step away from the role. Volker said it was whatever is best for the McCain Institute, the source said.

Cindy McCain, the late Sen. John McCain’s widow who also serves as chairwoman of the institute’s board of trustees, on Monday thanked Volker in a statement “for his dedication and hard work in helping to build the McCain Institute into the results-driven, action-oriented institution that it is today.”

The McCain Institute “implements programs and initiatives aimed at making a difference in people’s lives across a range of critical areas: leadership development, human rights, rule of law, national security, counterterrorism and combatting human trafficking,” according to the statement announcing Volker’s departure.

CNN’s Dana Bash, Nicole Gaouette, Kylie Atwood and Jennifer Hansler contributed to this report.