Bernie Sanders praised the “incredible courage” of Muhammad Ali not just as a boxer, but for taking a stand against the Vietnam War at the expense of a key moment in his career.

Sanders, appearing at a press conference in downtown Los Angeles, told reporters that “the reason Ali struck a chord in the hearts of so many Americans was not just his great boxing skill, it was his incredible courage, at a time when it was not popular to do so. Ali stood up and said, “I am opposed to the war in Vietnam, and I am not going to fight in that war.’ And that incredibly courageous decision cost him three and a half years of his prime fighting life. And cost him probably tens and tens of millions of dollars. That was the prime. That was when he was at his best.”

Ali died on Friday at the age of 74. He was temporarily banned from boxing competition after he refused to be drafted in 1967.

Sanders called himself “a bit of a boxing fan,” and called Ali “the most popular athlete in the modern history of the world.”

He also noted that at a time “when we are seeing growth in Islamophobia in this country, Ali as a young man made a decision that he wanted to become part of the Islamic faith. That is what he did.”

Sanders’ rival for the Democratic nomination, Hillary Clinton, wrote on Twitter that Ali “really was The Greatest — unmatched not just in power and skill, but also in courage and conscience. Thinking of his family.”

Donald Trump wrote that Ali was “a truly great champion and a wonderful guy. He will be missed by all!”

In December, Ali released a statement in which he said “We as Muslims have to stand up to those who use Islam to advance their own personal agenda. They have alienated many from learning about Islam. True Muslims know or should know that it goes against our religion to try and force Islam on anybody.”

Ali did not mention Trump in the statement, but it came just after Trump proposed banning Muslims from entering the United States. The statement mentioned “presidential candidates” proposing to ban Muslims from entering the country.

Sanders was campaigning in Los Angeles on Saturday, and will finish the day with a rally at the Los Angeles Memorial Coliseum and concert featuring Mark Foster, Ozomatli, Best Coast, Iration and Local Natives. Among the surrogate speakers are Josh Fox, Max Carver, Shailene Woodley, Susan Sarandon and Dick Van Dyke.