Georgia toughened identification requirements for absentee voting. Arizona authorized removing voters from the rolls if they do not cast a ballot at least once every two years. Florida and Georgia cut back sharply the use of drop boxes for mail-in ballots.

All of these new voting restrictions would have been rejected or at least softened if a federal civil rights protection from the 1960s were still intact, experts in election law said.

For decades, the heart of the landmark Voting Rights Act of 1965 was a practice known as preclearance, largely detailed under Section 5 of the statute. It forced states with a history of racial discrimination to seek approval from the Department of Justice before enacting new voting laws. Through preclearance, thousands of proposed voting changes were blocked by Justice Department lawyers in both Democratic and Republican administrations.

In 2013, however, Section 5 was hollowed out by the Supreme Court, as Chief Justice John G. Roberts Jr. wrote in a majority opinion that racial discrimination in voting no longer constituted a significant threat.

As Republican-led state legislatures have tightened voting rules after the 2020 election, new restrictions have been enacted or proposed in four states that are no longer required to seek approval before changing voting laws: Georgia, Arizona, Texas and Florida. Those new restrictions would almost certainly have been halted, stalled or altered had Section 5 still been in use, according to interviews with former federal prosecutors and a review by The New York Times of past civil rights actions by the Justice Department.

“There’s nothing subtle about what they’re trying to do,” said Tom Perez, the former head of the Justice Department’s civil rights division and a former chairman of the Democratic National Committee. “If Section 5 were still around, those laws would not see the light of day.”

The restoration of preclearance is now at the center of a debate in Congress over the passage of federal voting legislation.

On Tuesday, the House passed the John Lewis Voting Rights Advancement Act, which would restore preclearance in several states, among other changes. Attorney General Merrick B. Garland has urged Congress to revive preclearance, but Senate Republicans oppose such a move, and a filibuster in the Senate threatens to sink the bill before it can reach President Biden’s desk.