The Supreme Court has chipped away at the Voting Rights Act for 9 years. This case could be the next blow.

The Voting Rights Act of 1965 has been slowly whittled away over the last decade by the Supreme Court — and a case set to be heard in the fall could shrink the protections offered by the law to the smallest level yet.

The redistricting cycle preceding this year’s elections was the first in 50 years to take place without “preclearance” requirements under the law — a pillar of the Voting Rights Act as originally written, in which states with histories of discriminatory voting practices had to have new election...