Facing a crescendo of public criticism and a personal health crisis, United States Olympic Committee CEO Scott Blackmun abruptly resigned Wednesday.

Eight years into a tenure that was known for increasing American medal counts and booming revenues from broadcast rights and sponsorships, Blackmun’s resignation comes after sexual assault scandals from the U.S. gymnastics and swimming programs shook the Olympic movement – based in Colorado Springs – to its foundations. It also comes a month after Blackmun acknowledged his battle with prostate cancer.

“Given Scott’s current health situation, we have mutually agreed it is in the best interest of both Scott and the USOC that we identify new leadership so that we can immediately address the urgent initiatives ahead of us,” USOC Chairman Larry Probst said in a statement. “The USOC is at a critical point in its history. The important work that Scott started needs to continue and will require especially vigorous attention in light of Larry Nassar’s decades-long abuse of athletes affiliated with USA Gymnastics.”

Susanne Lyons, a current USOC board member, will take over as acting CEO of the organization.

“Serving the USOC and its many stakeholders and working with our board, our professional staff and many others who support the Olympic and Paralympic movements has not only been immensely rewarding, it has been an honor and the highlight of my professional life,” Blackmun said in a statement. “I am proud of what we have achieved as a team and am confident that Susanne will help the USOC continue to embody the Olympic spirit and champion Team USA athletes during this transition.”

Questions are rampant about how much Blackmun knew, and when, and how his organization handled allegations of sexual assaults on athletes in more than one Olympics sport, including on scores of gymnasts by Larry Nassar, a USA Gymnastics team physician who was sentenced earlier this year to up to 125 years in prison for decades of sexual abuse.

In a Dec. 21 letter to gold medal-winning gymnast and Nassar-victim McKayla Maroney, Blackmun apologized for the failure of the “Olympic family” to protect athletes, but said that he was not aware of the scope of the sex abuse claims before law enforcement got involved – and allegations made public in an Indianapolis Star expose – in 2016. Blackmun also claimed to have no knowledge of a previous settlement between USA Gymnastics and Maroney in a case involving the now-imprisoned former team doctor, nor of the gag order that Maroney’s December 2017 lawsuit sought to invalidate.

“And I want to be crystal clear on the topic of transparency,” Blackmun wrote in the letter, obtained by the Associated Press. “During my tenure as CEO, which began in 2010, we have never been, and will not be, party to any effort to conceal or keep confidential allegations or instances of sexual abuse.”

USOC has long claimed that it learned about potential abuse by the Team USA doctor in 2015, and followed protocol by reporting allegations to the FBI. The FBI, also, is now facing harsh criticism for its slow pace in pursuing the Nassar investigation, which only began in earnest after the stories about scandal in the Indianapolis newspaper.

Critics have called for Blackmun’s resignation, and in January the Olympics boss was driven to issue an open letter of apology.

“The purpose of this message is to tell all of Nassar’s victims and survivors, directly, how incredibly sorry we are,” Blackmun wrote in a message to Olympic athletes Jan. 24. “We have said it in other contexts, but we have not been direct enough with you. We are sorry for the pain caused by this terrible man, and sorry that you weren’t afforded a safe opportunity to pursue your sports dreams. The Olympic family is among those that have failed you.”

For many, though, the apology rang hollow, and too late.

Gold medal-winning gymnast Aly Raisman questioned the sincerity of the apology and commitment to reparations, when no representatives from USOC chose to be present in the courtroom during one sentencing hearing for Nassar.

Vince Finaldi, one of the attorneys representing McKayla Maroney, said Blackmun’s apology letter was “too little, too late.”

“I don’t believe for a second that Scott Blackmun sat down at his desk, drafted a letter and didn’t show it to anyone before releasing it,” said Finaldi, as reported in the New York Daily News. “You have to take it with a grain of salt. If your organization is dedicated to kids and sport, you have the obligation to step up and support them, not sit back in your office and send out some letter after the victims are done testifying when we’re years into this mess.”

Allegations of sexual abuse weren’t limited to gymnastics. In a sweeping February report, the Orange County Register in California revealed that more than 250 coaches and officials with USA Swimming have been arrested, charged or disciplined for alleged sexual misconduct with swimmers under the age of 18.

Jim Sheehan, board chairman of USA Swimming, seemed stunned at Blackmun’s resignation Wednesday.

“I actually don’t have anything to say on that,” Sheehan said.

The compounding sexual assault allegations led a group of prominent Olympic boosters to call for Blackmun to leave.

“Scott Blackmun has allowed one of the country’s largest youth-serving organizations to avoid basic child protection measures, such as prohibitions on adults being alone with children,” said Nancy Hogshead-Makar, a leader in the group dubbed Committee to Restore Integrity to the USOC and a former Olympic champion swimmer. “He has instructed the USOC to sit on the sidelines when athletes have been sexually abused. He has ignored the pleas of athletes, all in order to serve the USOC’s corporate interests of limited civil liability. He does not deserve to lead our Olympic Team.”

On Wednesday, Hogshead-Makar took to Twitter to react to the Blackmun news.

“He knew the risk of #SexualAbuse and he didn’t enact basic #ChildProtection policies or educate the membership about how to prevent it,” she wrote. “His legacy will be that he failed athletes.”

A Dartmouth-educated attorney, Blackmun was the Olympic Committee’s in-house lawyer and interim CEO before he departed in 2001 to become the chief operating officer of Anschutz Entertainment Group. He came back to the committee in 2010 and led a revolution in revenue. With surging payments for television rights and sponsorships, the committee hauled in $920 million from 2013 to 2016, according to a report issued to Congress.

He’s credited with repairing relations between the U.S. contingent and the International Olympic Committee and led the charge that secured the return of the games to American soil with the 2028 summer Olympics set for Los Angeles.

Blackmun also saw success on the podium for America’s Olympians.

“Under Blackmun’s direction, Team USA topped the overall medal counts at the 2010, 2012 and 2016 Olympic Games, and won the most medals at any Olympic Winter Games held outside North America in 2014,” the USOC said on its website.

But the American team struggled in South Korea, bringing home 23 medals including nine golds against the 28 medals earned by Americans in the 2014 winter games and 36 in 2010.

Any medal count in 2018, though, was overshadowed by the growing sexual assault scandal in Olympic sports.

Blackmun in January commissioned an internal probe into the gymnastics incidents.

“The USOC has decided to launch an investigation by an independent third party to examine how an abuse of this proportion could have gone undetected for so long,” Blackmun wrote. “We need to know when complaints were brought forward and to who.”

Before the sexual assault scandals exploded, Blackmun was seen as a crusader for cleaning up the games.

Shortly after getting the top USOC job, Blackmun launched an effort to stamp out sexual assault and support victims. Those efforts culminated last year with the launch of the U.S. Center for Safe Sport, a Denver-based non-profit independent of the Olympic Committee that’s charged with investigating complaints, educating athletes and supporting victims.

In a Gazette column last year, Blackmun touted the work.

“Could we do more? Always. Should we have begun acting before 2010? I wish we had,” Blackmun wrote. “But to suggest that the USOC is not diligently and effectively working to solve this problem is unfair to the USOC and misleading to the American public.”

Blackmun’s tenure also includes a legacy that will be visible on the downtown Colorado Springs skyline for decades to come.

The Olympics chief helped spearhead an effort to bring the U.S. Olympics Museum and Hall of Fame here. The project broke ground last year.

“The Olympic movement is different,” Blackmun said at the time. “It’s not like other sporting events, because it’s values-based. That combined with the fact that our athletes are representing their nation is why more people watch the Olympic Games than any other property. And it’s why people are going to come to Colorado Springs to be a part of it. We’re grateful at the USOC to support this great project.”