By Jason Lange and James Oliphant

The vast majority of protesters have been peaceful, but a “small minority” were putting people at risk and harming the very communities the protests are intended to help, Obama wrote in an online essay posted on Medium.

Obama, a Democrat who served two terms as president prior to Republican Donald Trump’s administration, said the violence was “compounding the destruction of neighborhoods that are often already short on services and investment and detracting from the larger cause.”

The United States has been rocked by six straight nights of tumult over the death last week of a black man in Minneapolis, George Floyd, after a white police officer pinned him to the ground by kneeling on his neck.

Obama’s latest remarks came three days after his first comments on the Floyd case, which called for justice but did not mention the violent nature of some protests. His shift in tone on Monday came as some protesters have set fires, smashed windows and looted stores, forcing mayors in large cities to impose nighttime curfews.

Joe Biden, the likely Democratic nominee for president who served as Obama’s vice president, on Sunday also called for an end to the violence. “Protesting such brutality is right and necessary,” Biden said in a statement. “But burning down communities and needless destruction is not.”

Biden will face Trump in the Nov. 3 general election.

In his essay, Obama urged those seeking reform to embrace politics, arguing that electing new leaders on the national and local levels would bring about change.

“… Eventually, aspirations have to be translated into specific laws and institutional practices — and in a democracy, that only happens when we elect government officials who are responsive to our demands,” he said.

(Reporting by Jason Lange and James Oliphant in Washington; editing by Jonathan Oatis)