As long as politicians are entrusted with drawing legislative maps, they will use their pen to gain partisan advantage. Courts generally do not interfere with that process, but there are limits to this where race is involved. The problem is figuring out which motive — race or partisanship — underlies the redistricting. On Wednesday, the Supreme Court considered this issue in a thorny case that could have significant implications for the future of the Voting Rights Act.

The main legal question before the justices was whether Alabama lawmakers had paid too much attention to race when they redrew the state’s district lines.

The 1965 voting law requires states to create districts where minorities can elect candidates of their choice, specifically in places where whites and blacks tend to pick different candidates. That’s clearly the case in Alabama, where, in 2008, Barack Obama received 98 percent of the black vote and 10 percent of the white vote.

The Constitution also requires that state legislative districts contain roughly equal populations.

Following the 2010 census, the Alabama Legislature, which only recently came under Republican control, drew new district lines that put tens of thousands of additional black voters into districts that already had a black majority. The lawmakers said they had no choice, that many of the districts had lost residents and, they believed, the Voting Rights Act required them to keep the percentage of black voters in each district the same as before.