The Voting Rights Act – a cherished safeguard for minority voters since 1965 – has been under siege for two years and this week faces one of its toughest tests on an apparent path to the U.S. Supreme Court.

Twenty-five hours of argument, starting on Monday and spread over five days, will help the judges of the U.S. District Court for the District of Columbia decide whether Texas can require voters to present a photo identification at the polls.

Formulated at a time of racial turmoil, the Voting Rights Act passed 77-19 in the U.S. Senate and 333-85 in the House of Representatives. The votes transcended party lines to protect black voters of all political ideals.

Ever since, it has served as the U.S. government’s chief check on the fairness of election rules imposed by local governments.

While it passed with bipartisan support more than 45 years ago, a shift in political preferences along racial lines has turned the landmark piece of civil rights era legislation into a highly charged political issue.