For months, the Justice Department has largely been silent as Republican-dominated legislatures in state after state made it harder for minorities, poor people and other Democratic-leaning groups to vote. On Tuesday, however, Attorney General Eric Holder Jr. spoke out forcefully and promised to use the full weight of his department to ensure that new electoral laws are not discriminatory. To live up to that vow, he will have his hands full.

Republican lawmakers in more than a dozen states have recently enacted laws designed to limit Americans’ access to the polls, often concentrating on voters — blacks, Hispanics, students and the poor — who showed up in large numbers in 2008 to elect Barack Obama. They have imposed strict voter-ID requirements, knowing that millions of people cannot easily meet them; eliminated early voting periods; and restricted registration drives. (Voter ID laws have been introduced in at least 34 states.)

These efforts, Mr. Holder said, have led many Americans “to believe that we are failing to live up to one of our nation’s most noble, and essential, ideals.” Quoting John Lewis, the Georgia congressman who was beaten in the 1960s while advocating voting rights for blacks, he said those rights are under attack by “a deliberate and systematic attempt” to prevent millions of voters from exercising their constitutional right to engage in democracy.

It was very encouraging to hear Mr. Holder recognize the depth of the assault on a fundamental constitutional right. The question is how far he will use his department’s power to stop it. On that subject, he was a little vague, promising to use his power under Section 5 of the Voting Rights Act to object to any law that is discriminatory, citing new laws in Texas, South Carolina and Florida.