What exactly did the court rule?
In a 5-4 decision, the court decided that Section 4 of the Voting Rights Act is unconstitutional. Section 4 dictates which parts of the country must receive pre-clearance before election laws can be changed there (more on that below).
“Section 4’s formula is unconstitutional in light of current conditions,” Chief Justice John Roberts wrote. “Coverage today is based on decades-old data and eradicated practices.”
So in a nutshell, it will fall to Congress to come up with a new formula based on current conditions for figuring out which jurisdictions should be subject to pre-clearance.
Back up a second. What is the Voting Rights Act?
Signed into law by President Lyndon Johnson in 1965, the sweeping legislation was designed to prevent racially discriminatory voting practices.
You mentioned Section 4. What is Section 5? There was a lot of buzz about that leading up to Tuesday's decision.
This is the part of the Voting Rights Act that makes it legal for areas with a history of racial discrimination to receive pre-clearance from the Justice Department or a federal court before making any voting law changes. The court did not pass judgement on Section 5 Tuesday, which means the Justice Department still has authority to decide which jurisdictions need pre-clearance. But the existing formula can no longer be used to decide which areas those are. So the reality is that absent new guidelines from Congress, Section 5 doesn't apply anywhere moving forward.
Which states have been subject to Section 5?
Alabama, which was the subject of the Supreme Court case, and eight other complete states as well as some other selected jurisdictions elsewhere have been subject to Section 5. Most of the the states are in the South. In light of Tuesday's decision, these areas effectively no longer require pre-clearance.
Over the years, Congress has reauthorized Section 5 several times, most recently in 2006.
Why did opponents of Section 5 say?
They say that it is outdated. “The violence, intimidation and subterfuge that led Congress to pass Section 5 and this court to uphold it no longer remains,” said the Shelby County challenge. And as NPR noted, the formula still relies on election data from 1972. Tuesday's court decision involved Shleby County, Alabama. Shelby County Attorney Frank Ellis explained the opposition in this CBS News report:
They believe it’s still a necessary preventive measure against changes to voter ID laws, district lines and other adjustments that could threaten the rights of minority voters. President Obama, who believes Section 5 should be kept in place, summed it up like this in an interview with Joe Madison of SiriusXM Radio:
All eyes will be on Congress. The question is whether lawmakers will come up with a new formula to decide which areas will be subject to pre-clearance under Section 5.
"We issue no holding on §5 itself, only on the coverage formula. Congress may draft another formula based on current conditions," reads Tuesday's decision.
Based on the major disagreements seizing Congress these days, there is no reason to expect accord on the matter anytime soon, though.