Republican-led legislatures in several states including Georgia, Florida and Iowa have passed laws imposing new voting restrictions, and Texas, New Hampshire, Arizona and Michigan, among other states, are considering changes to their electoral systems.

At the same time, hopes have dimmed on the left that Congress will pass two major election bills after Senator Joe Manchin III, Democrat of West Virginia, said he would not support abolishing the filibuster to advance such measures.

Mr. Garland has said that protecting the right to vote is one of his top priorities as attorney general, and his top lieutenants include high-profile voting rights advocates such as Vanita Gupta, the department’s No. 3 official, and Kristen Clarke, the head of the Civil Rights Division. The division currently has about a dozen employees on its enforcement staff, which is focused on protecting the right to vote, according to a department official familiar with the staff.

Despite his pledge, Mr. Garland is still limited in what he can do unless Democrats in Congress somehow manage to pass new voter protection laws. He can sue states that are found to have violated any of the nation’s four major federal voting rights laws. He can notify state and local governments when he believes that their procedures violate federal law. And federal prosecutors can charge people who are found to have intimidated voters, a federal crime.

The Justice Department’s most powerful tool, the Voting Rights Act, was significantly weakened by a 2013 Supreme Court decision that struck down pieces of the act forcing states with legacies of racial discrimination to receive Justice Department approval before they could change their voting laws.

Now the department can only sue after a law has been passed and found to violate the act, meaning that a restrictive law could stand through multiple election cycles as litigation winds its way through the courts.

Any new steps to protect voting rights are unlikely to move quickly, said Joanna Lydgate, a former deputy attorney general of Massachusetts who co-founded the States United Democracy Center. “People will need to be patient,” she said.