For more than a decade, Lance Armstrong has attacked his accusers with the same ferocity that he attacked the grueling mountain terrain of the Tour de France, insisting that his record seven championships in cycling’s most prestigious event were earned honestly, despite persistent rumors of banned drugs.

On Wednesday, having been exposed by teammates who formerly stood by him and labeled a “serial cheat” by the U.S. Anti-Doping Agency, Armstrong conceded for the first time publicly that the controversy surrounding his cycling career stands to damage his charitable work. Armstrong also lost the support of his longtime corporate backer, Nike, which said it was terminating its contract with the disgraced champion.

Armstrong, 41, announced his resignation as chairman of the Livestrong Foundation he created on behalf of cancer patients “to spare the foundation any negative effects as a result of controversy surrounding my cycling career.”

Armstrong has yet to address to damning charges against him: that all of his cycling achievements from 1999 on, in effect, were fraudulent.

Nike, which has been the primary corporate backer of Armstrong’s charitable work, will continue its support of the Livestrong Foundation. But Armstrong himself will no longer be compensated as a Nike pitchman in the wake of USADA’s scathing report detailing years of doping — his image deemed too tainted even for a company that has stood by its star athletes in times of controversy, whether that be the 2003 sexual assault charge against the NBA’s Kobe Bryant or the reports of chronic philandering that ended Tiger Woods’s marriage and temporarily halted his golf career.

Nike’s statement about Armstrong read: “Due to the seemingly insurmountable evidence that Lance Armstrong participated in doping and misled Nike for more than a decade, it is with great sadness that we have terminated our contract with him.”

It was a complete reversal of Nike’s supportive stance in the wake of the Oct. 10 airing of USADA’s report, known as a “reasoned decision,” which enumerated the evidence and reasons why the agency stripped Armstrong of his seven Tour de France titles and banned him from competition on Aug. 24 when he refused to face the charges against him.

The 202-page report, which was backed by more than 1,000 pages of documents and testimony, said Armstrong was the driving force behind “the most sophisticated, professionalized and successful doping program that sport has ever seen” and had won his Tour titles “start to finish” by doping.

It relied on the testimony of 26 witnesses, including 11 of Armstrong’s former teammates. Some among them, such as George Hincapie and Levi Leipheimer, confessed that they, too, had used banned substances as part of their testimony against Armstrong. The report included detailed, first-hand accounts of Armstrong not only taking banned substances such as testosterone and EPO and undergoing blood transfusion but also pressuring teammates on the U.S. Postal Service cycling team to dope so they could more effectively propel him to victory. It recounted elaborate subterfuges used to ferry drugs to Armstrong at key stages of the Tour, as well as ruses to evade drug tests. And it portrayed Armstrong as a vengeful bully who threatened those in position to testify against him.

To be sure, Armstrong will remain a hero in the view of many who have battled cancer or other serious illness and drawn inspiration from his personal narrative. A 16-year survivor of testicular cancer, he will continue to serve on Livestrong’s 15-person board.

But Wednesday’s developments suggest that Armstrong’s value as a corporate spokesman has suffered a major hit, dimming his financial prospects going forward in much the same way that USADA’s voluminous report gutted his cycling triumphs of 1999 to 2005.

“Nike had no choice but to cut ties with him, and he needed to disassociate himself with the foundation,” crisis-management specialist Ashley McCown, president of Solomon McCown & Company, said in a telephone interview Wednesday.

“Lance Armstrong is a brand, and Nike is a premiere brand. He is now a toxic asset that cannot be associated with. There is too much of a chance for Nike’s fine reputation to be tarnished. Lance is damaged goods. The actions today speak volumes about that.”

According to Katherine McLane, vice president of communications and external affairs for the Lance Armstrong Foundation (known more widely as the Livestrong Foundation), donations increased after USADA stripped Armstrong of his Tour de France titles and banned him from cycling in August.

Asked Wednesday why Armstrong decided to step down as chairman, McLane said: “It was something he was considering in order to inoculate the foundation from any spillover effect as a result of the controversy surrounding his cycling career. He made the decision it would be better to step down as the titular head of the organization.”

The USADA report is currently being reviewed by cycling’s international governing body, the UCI. It has until Oct. 31 to either affirm USADA’s punishment of Armstrong or appeal its actions to the Court of Arbitration for Sport.

Meantime, the International Olympic Committee is believed to be waiting for UCI’s decision before announcing whether it will revoke Armstrong’s bronze medal from the 2000 Sydney Olympics, which was achieved during the period in which USADA concluded that Armstrong doped his way to cycling glory.