"Let me be clear: while this country has indeed changed, and real progress has been made — we are not yet at the point where the most vital part of the Voting Rights Act can be described as unnecessary or a product of a flawed political process," Holder said. "That’s why today’s Justice Department has vigorously defended Section 5 as an indispensable — and constitutional — tool for eradicating discriminatory electoral processes."

Section 5 of the Voting Rights Act requires municipalities with a history of disenfranchisement efforts to pre-clear changes to voting practices with the Justice Department or a federal court. The provision was designed to prevent states from instituting poll taxes, literary tests or other efforts to keep minority voters from the polls that might later be ruled unconstitutional from doing so before an election.

In oral arguments heard earlier this year, the Supreme Court seemed primed to overturn Section 5. In 2009, swing justices John Roberts and Anthony Kennedy ruled in favor of allowing a Texas jurisdiction to apply for an exemption to Section 5, and the majority decision hinted that a wholesale challenge could be successful.

Interestingly, Holder's comments seemed to break from comments made by President Obama, who in February said that that while Section 5 had been historically important in enfranchising African-American voters, “it's not the only tool we have.”

“It's a critical tool, it's not the only tool,” Obama told “The Black Eagle” radio show on SiriusXM.

On Thursday, Holder said the Department of Justice would continue to aggressively pursue voting rights protections even if the Supreme Court ultimately does strike down Section 5.

"No matter the outcome, the Department of Justice will remain committed to the aggressive and appropriate enforcement of all voting and civil rights protections, including every part of the Voting Rights Act," Holder said. "And we are eager to work with elections administrators and elected leaders throughout the country to consider policies aimed at making more fair — and modernizing — our voting systems; ensuring that all eligible citizens have equal access to the ballot; and preventing and punishing fraudulent voting practices — however rare."