The Rev. Jesse Jackson, the civil rights leader and former presidential candidate, announced Friday that he has Parkinson’s disease.

Jackson, 76, said he had found it “increasingly difficult to perform routine tasks” and get around in recent years. After initially resisting due to his work, Jackson said, he relented and sought medical testing.

“Recognition of the effects of this disease on me has been painful, and I have been slow to grasp the gravity of it,” Jackson said in a statement released through the Rainbow PUSH Coalition, his social change group. “For me, a Parkinson’s diagnosis is not a stop sign but rather a signal that I must make lifestyle changes and dedicate myself to physical therapy in hopes of slowing the disease’s progression.”

Jackson was diagnosed with the disease in 2015, according to a statement released by Northwestern Medicine in Chicago. “Since that time, Northwestern has been treating Jackson in an outpatient setting.”

Jackson remains an active presence in American life and politics. Last year, he shuttled across the country speaking and registering people to vote, saying that people “are very motivated when we are inspired.”

He is one of the best-known and influential activists of the civil rights era, extending the movement into national politics with his presidential campaigns in the 1980s that have since been viewed as paving the way for former president Barack Obama’s election as the first black president in 2008. Jackson’s efforts added millions of African-Americans to the voter rolls and increased the influence of black political leaders and strategists in the Democratic Party.

In 1988, during his second bid for the Democratic nomination, Jackson finished second to Massachusetts Gov. Michael Dukakis. Ron Brown, who led Jackson’s team at the Democratic National Convention in 1988, later became the party’s first African-American chairman. Former president Bill Clinton appointed Brown as the first black secretary of the Commerce Department. He was killed in a plane while in office.

Jackson surprised many political observers that he was able to get support from some working-class whites with an economic message not unlike the one that the insurgent campaign of Sen. Bernie Sanders, D-Vt., in last year’s Democratic presidential primary.

During an appearance in late summer on HBO’s “Real Time,” Jackson reiterated that message when host Bill Maher noted that a significant number of President Trump’s white working-class supporters feel that they are victims of racial discrimination. “Seventy-eight percent of Americans live paycheck to paycheck; 51 percent of Americans make $30,000 a year or less,” he said, adding that many had been left behind in the fast-changing global economy. As a result, Jackson said, some of those working-class whites have “a deep sense of anxiety … they feel locked out and they start scapegoating.” He said that politicians like Trump exploit their fears but “there is tremendous economic anxiety that must not be ignored.”

Donna Brazile, who launched her career in national politics as Jackson’s field director in 1984, later called Jackson’s legacy a transformative one for the Democratic Party. “He made it possible not just for blacks to sit at the black desk, but to sit at every desk in American politics,” Brazile told The Washington Post in 2008. She was manager of Al Gore’s 2000 presidential bid, the first African American woman to run a major party’s presidential campaign.

In a brief interview Friday, Brazile said she was praying for her friend and longtime mentor.

“If there is anyone who can beat the odds and rise above the challenges, it’s Rev. Jackson,” she said, adding that she had seen him a few months ago and she asked about his health he said he felt fine. “He’s a strong man, he’s a determined man, a man of faith and a powerful, powerful force for good.”

The Rev. Al Sharpton, who once worked for Jackson, said Friday he had spent recent days in New York with the man he described as his mentor, and he praised Jackson’s work and legacy on civil rights issues and in electoral politics.

“He changed the nation,” Sharpton said in a video statement. “He served in ways he never got credit [for]. No one in our lifetime served longer and stronger. We pray for him because he’s given his life for us.”

Andrew Young, the United States ambassador to the United Nations and former mayor of Atlanta, was stunned by the news about Jackson, with whom he worked alongside in the Southern Christian Leadership Conference in the 1960s. “I saw him a couple of months ago. He seemed to be very healthy. He’s always on the go and he always speaks in a very strong voice,” Young said in a phone interview Friday.

In his announcement Friday, Jackson described Parkinson’s as “a disease that bested my father” and pledged to use his platform and voice to seek a cure for the illness. According to the Centers for Disease Control and Prevention, Parkinson’s is the second-most-common neurodegenerative disorder, trailing only Alzheimer’s disease.

Parkinson’s affects the parts of the brain that control the body’s motor system. The National Parkinson Foundation’s web site states that symptoms develop slowly over time and people with the disease could experience tremors in their hands, rigidity of their limbs and difficulty walking. There is treatment to slow the progression of the disease, but there is no cure for Parkinson’s, which itself is not fatal, but can lead to serious complications that can lead to death. People can live for decades with Parkinson’s.

“I will continue to try to instill hope in the hopeless, expand our democracy to the disenfranchised and free innocent prisoners around the world,” Jackson wrote, adding that he would also work on a memoir. “I steadfastly affirm that I would rather wear out than rust out.”