Saturday is the 51st anniversary of the Voting Rights Act, a major piece of civil rights legislation, and one that has prevented discriminatory policies that keep minorities from the voting booth. But changes in the original law mean that we mark the occasion without two key provisions, making 2016 the first presidential election without the full protection of the original law.

In 2013, the Supreme Court invalidated section 4 of the VRA in Shelby County v. Holder in a 5-4 ruling. Section 4 was the formula determining which states and localities had to go through a preclearance process, which is outlined in Section 5. “Preclearance” was the process whereby states and localities that had a history of discriminatory voting laws needed federal approval before changing election laws. Since the sections worked hand in hand, without Section 4, the coverage formula, Section 5 became inoperative.

READ MORE: North Carolina voter ID law overturned for ‘racially discriminatory intent’

Georgia Rep. John Lewis said in an Washington Post op-ed on the day of the decision that the purpose of the Voting Rights Act was “not to increase the numbers of minority voters or elected officials. That is a byproduct of its effectiveness. The purpose of the act is to stop discriminatory practices from becoming law.”

Since 2013, states with a history of discrimination have been able to change voting laws without federal oversight. Since then, the U.S. has seen sweeping changes, with many states adopting stricter regulations, such as mandatory voter ID and eliminating pre-registration. Fifteen states have tougher voting laws in place for a presidential election for the first time.

Here’s a guide to the changes and what they mean for voters:

Which states, previously covered under Section 5, have passed stricter voting laws after the 2013 SCOTUS decision?

Six states have passed new voting laws after Shelby County v. Holder; those states include Alabama, Arizona, Georgia, Mississippi, Texas, and Virginia. Laws range from strict voter ID requirements to the elimination of same-day voter registration and out-of-precinct voting.

Why are states passing stricter voting laws?

Depends on whom you ask.

Supporters of these stricter voting laws say they are intended to combat voter fraud. “My view is that it should be easy to vote but hard to cheat,” said Kansas Secretary of State Kris Kobach in a Washington Post article.

Election law experts note there is no significant evidence of voter fraud. Rick Hasen, professor of Law at University of California, Irvine says the voting fraud America sees, which is rare, includes vote-counting by elected officials or issues surrounding absentee ballots.

Those who oppose stricter laws say they are a response to an increase in minority voting power. The black turnout exceeded white turnout for the first time in the 2012 election.

Restrictive voting laws were blocked in court during the 2012 election, but the large turnout inspired backlash against minority voters, according to Ari Berman, senior writer at the Nation and author of Give Us the Ballot. And since a higher percentage of minorities vote Democrat, those against restrictive laws say voting rights have been politicized. (Though Deborah Archer, professor at New York University Law contends that “the fact that it has a partisan benefit doesn’t negate the intent or impact.”)

Which states were required to have preclearance under Section 5, and what was the formula?

Section 5 covered 15 states. Congress was responsible for revising and updating the coverage formula, established in Section 4. States under the 1965 coverage formula had:

Voter turnout or registration rates lower than 50 percent in the 1964 presidential election and

laws that discouraged voters like literacy tests or poll taxes.

In 1970, Congress revised the coverage formula with data from the 1968 presidential election, and in 1975, revised data to reflect the 1972 election. That included the growing population of minority language voters, meaning that states where at least 5 percent of voting population spoke another language but had English-only ballots fell under Section 5.

Have these new voting laws been challenged?

This summer, voting laws in six states — North Carolina, North Dakota, Wisconsin, Kansas, Texas and Michigan — experienced pushback from the courts. Some courts have gone as far as to question the intent of the voting laws, reckoning that some laws are not improving democracy but are used to discriminate. A federal appeals court struck down North Carolina’s voter ID law for having discriminatory intent, whereas other courts challenging similar laws in other states said the impact disenfranchised minority voters.

It’s not enough to just look at the state’s litigation, to see what the law’s articulated reasoning is, and take that at face value, said Wendy Weiser of the Brennan School of Justice. Now courts are now looking at the justifications — the intent — behind it, she said.

Weiser predicts we will see more voting rights cases trickle through, most likely from Arizona, Kansas, Wisconsin and Alabama. Just this past Thursday, the North Carolina governor’s request to put that same voter ID ruling on hold, pending a request for the Supreme Court to review the decision, was denied by a 4th Circuit Court of Appeals.

Does preclearance in Section 5 have a chance of being reinstated?

Congress has introduced two bills to restore VRA’s preclearance — the Voting Rights Amendment Act and the Voting Rights Advancement Act — which would look at voting rights violations from the last 15 years, and the other from the last 25 years, respectively. Neither has made much headway.

How will this affect the 2016 presidential election?

It’s unclear. Likelier than not, these stricter voting laws will impact the election results but scholars can only speculate to what degree. When voting laws change, people are not always attuned to it, said Ari Berman. Some people won’t know that same-day registration has been eliminated and that they can’t register at the polls anymore, he said.