Half a century after the U.S. passed a law intended to give all its citizens equal access to the voting booth, President Barack Obama said that protection is at risk.

"In practice we've still got problems," Obama said Thursday at a White House event he hosted with Attorney General Loretta Lynch and Rep. John Lewis, a Georgia Democrat who was a leader in the civil rights movement. "On the ground there are still too many ways in which people are discouraged from voting."

The remarks came on the 50th anniversary of President Lyndon B. Johnson signing the Voting Rights Act in 1965. The law prohibited states from enacting policies aimed at preventing blacks from voting, including poll taxes, literacy tests and civics quizzes.