WASHINGTON — For the first time since the days of poll taxes and literacy tests a half-century ago, the Justice Department will be sharply restricted in how it can deploy some of its most powerful weapons to deter voter intimidation in the presidential election.
Because of a Supreme Court ruling three years ago, the department will send special election observers inside polling places in parts of only four states on Election Day, a significant drop from 2012, when it sent observers to jurisdictions in 13 states.
And in a departure from a decades-old practice, observers will be sent to only one state in the South, where a history of discriminatory voting practices once made six states subject to special federal scrutiny.
The pullback worries civil rights advocates, who say that Donald Trump's call for his supporters to monitor a "rigged" electoral system could lead to intimidation of minority voters at polling places.
Since 1965, federal officials have sent about 32,000 observers to jurisdictions with histories of harassing minority voters or even outright denying them access to the ballot. But officials say their hands are now tied by a 2013 Supreme Court decision that gutted the heart of the Voting Rights Act of 1965.
As a result of that decision, in Shelby County v. Holder, the Justice Department will send observers only to jurisdictions where it already has court approval. That encompasses seven counties or jurisdictions in Alaska, California, Louisiana and New York.
"We do not want to be in the position we're in," Vanita Gupta, the top civil rights official at the Justice Department, said in an interview. "There's no doubt that we're going to be spread thinner," she added, "but our hope and our intention is that we are going to have a very robust monitoring program" on Election Day.
The Justice Department will still send election monitors — expected to number in the hundreds — outside polling places in about 25 states, which will be announced just before Election Day. But unlike the specially trained election observers, monitors are not allowed inside unless local election officials invite them.
"The federal observer program has really been a hallmark of the Justice Department's voting rights work," said Kristen Clarke, the director of the Lawyers' Committee for Civil Rights Under Law. That effort "has really come to a grinding halt," she said, "and that's a game changer this election cycle."
The Voting Rights Act was passed by Congress and signed into law by President Lyndon B. Johnson at the height of the civil rights era. In the Shelby County decision, Chief Justice John Roberts wrote that "our country has changed" since those days of rampant voter discrimination.
The decision — which freed nine states, mostly in the South, to change their election laws without advance federal approval — unleashed a wave of new voting arrangements in scores of jurisdictions. Civil rights advocates argue that those changes, including voter identification requirements that have since been overturned, have been intended to make it more difficult for blacks, Hispanics and other minorities to vote.
The Shelby ruling did not specifically address the Justice Department's authority to send observers inside polling places. But Gupta said department lawyers had interpreted the decision to mean that officials could send observers only into jurisdictions where there was already a relevant court order regarding voting practices.
That broad interpretation has puzzled some legal scholars on both the left and the right.
"I was a little surprised by the Justice Department's decision, to be honest," said Derek T. Muller, a conservative scholar on election law at Pepperdine University School of Law.
Muller said he believed that the Justice Department could legally send observers to jurisdictions not specifically covered by court orders.
"Until a court tells them otherwise, that provision is still on the books," he said.
In any case, the restrictive new voting procedures enacted after the Shelby ruling threaten to have a chilling effect on minorities, particularly if Trump's supporters show up at polling places to challenge voters' status, said Nina Perales, the litigation director for Maldef, a Hispanic civil rights group.
"These things can have a very negative effect on registered voters — by challenging them and their right to vote," she said in an interview. "We've definitely been there before when it comes to harassing Latino voters and accusing them of committing fraud."
In Phoenix, a heavily Hispanic city, voters faced hourslong waits during primary elections in March after Maricopa County officials decided to close 70 percent of polling places to save money.
Arizona was one of the nine states that the Supreme Court freed from getting advance approval for changes in voting procedures. Gupta, the Justice Department official, said that if federal officials could have reviewed the changes beforehand, it might have made "a huge difference" and saved voters significant aggravation.
"We have never hidden the fact," Gupta said, "that the cost of the Shelby County decision has been quite grave for the tools that the Justice Department has."
Attorney General Loretta Lynch sought to assure voters in a video posted last week by the Justice Department that the setbacks of the Shelby decision would not deter federal officials.
"We stand ready to ensure that every voter can cast his or her ballot free of unlawful intimidation, discrimination or obstruction," she said.