President Lyndon B. Johnson goes to shake Martin Luther King Jr.’s hand on Aug. 6, 1965, at the Signing of the Voting Rights Act in the Capitol Rotunda. (Yoichi R. Okamoto/LBJ Library)

In a Winston-Salem, N.C. federal courthouse, closing arguments are taking place this morning in a hotly-contested trial over North Carolina’s restrictive voting law. The U.S. Department of Justice and civil rights groups say that the 2013 law, passed by a Republican legislature over the objections of Democrats, violates the Voting Rights Act and the Constitution. The state defends its law as necessary to prevent voter fraud and keep public confidence in the electoral process.

As the New York Times explained, “The contested measures reduced early voting days, ended same-day registration, ended out-of-precinct voting and halted the preregistration of 16- and 17-year-old high school students. These measures had been adopted in the past 15 years to increase voter participation and were disproportionately used by black, Hispanic and younger voters.”

Since the Voting Rights Act passed 50 years ago — on Aug. 6, 1965 — there have been many legal disputes over the extent of court protection for minority voting. The outcome of this one, like many cases before it, may depend upon how well murky law matches up with political science evidence.

Political scientists have long played a major role in important redistricting disputes under the Voting Rights Act. The United States Supreme Court laid down rules for adjudicating those disputes in 1986, with its decision in Thornburg v. Gingles. In Thornburg, the court declared that there are two essential questions to be answered under Section 2 of the Act:

  1. How “racially polarized” is the voting? In other words, how strongly do white voters prefer one set of candidates and minority voters a different set of candidates? Typically a court will find racially polarized voting when those challenging the districting prove that white voters in an area tend to vote together to usually defeat the preferred choice of a cohesive group of African-American, Latino, or other minority voters.
  2. Do protected minority voters constitute a large and compact enough group to require the creation of districts in which they can elect a representative of their choice? If minority voters live in the same area and are have enough voters to make up a district where they can elect a representative of their choice, then a court, after examining what the courts call the “totality of the circumstances” can mandate the drawing of minority opportunity districts.

The Voting Rights Act itself does not explicitly lay out the Gingles test. The statute is deliberately murky, part of a compromise engineered by former senator Bob Dole. Section 2’s language prevents the right to vote from being “abridged” on account of race, color, or membership in a protected language minority group. Challengers prove abridgement when, “based on the totality of circumstances, it is shown that the political processes leading to nomination or election in the State or political subdivision are not equally open to participation by members of a class of citizens protected by [the Act] in that its members have less opportunity than other members of the electorate to participate in the political process and to elect representatives of their choice.” A state doesn’t have to intend to discriminate against a minority group to violate Section 2; a law merely has to have that effect.

[States with higher black turnout are more likely to restrict voting]

The Gingles test has been relatively easily used in vote dilution redistricting cases, where a white majority bands together to defeat the votes of minority voters. But Gingles doesn’t directly apply in cases like the one in North Carolina, where the question is not about dilution but vote denial: whether it is illegal to pass laws that make it harder to register or vote.

The 2013 North Carolina law being challenged by the U.S. Department of Justice and civil rights plaintiffs is a classic vote denial law. It requires each voter to have a specific kind of photographic identification to vote; it ended same-day voter registration, requiring voters to register 20 days in advance; it cut back early voting from 17 to 10 days; it ended preregistration of 16- and 17-year-olds, a program which made those preregistered automatically eligible to vote upon turning 18; and it stopped counting votes cast by those who mistakenly voted in the wrong precinct, even if the voter did so because a poll worker made a mistake. (Because North Carolina considerably relaxed its voter ID requirements on the eve of trial, allowing voters to cast a ballot in some circumstances without meeting the strict ID requirements, the challenge to that part of the law has been put on hold.)

Plaintiffs argue this combination of changes count as an “abridgement” of the right to vote on account of race in violation of Section 2. But how should Judge Schroeder decide whether these changes abridge the rights of minority voters? There are both legal and empirical issues.

[N.C. case represents pivotal point of voting debate]

Legally, courts have been dividing over the Section 2 standard in vote denial cases. Ohio state law professor (and my casebook co-author) Dan Tokaji argues that the voting rights plaintiffs in these cases should have to prove that the challenged practice has a disparate impact on minority voters and that the disparate impact can be traced to the challenged practice’s interaction with social and historical conditions, including but not limited to intentional discrimination by the state. If plaintiffs do so, then courts should balance the harm to minority voters against the state’s interests in the law.

Political science has much to say on all three parts of Tokaji’s test. As for disparate impact, North Carolina argues that its new law did not depress turnout because turnout among African-American voters went up in 2014 compared to 2010, which are comparable midterm election years. Plaintiffs argue that looking just at total turnout is too simple, as lots of factors determine turnout (such as the fact that 2014 featured a very competitive U.S. Senate race between Kay Hagan and Tom Tillis).

Plaintiffs point to the fact that African Americans in North Carolina were heavier users than others of early voting and same-day voter registration — and so ending both of those has a disparate impact, affecting them more heavily. The two sides are arguing over whether taking these tools away will actually lead to a decline in African-American turnout overall over time.

Tokaji’s next factor is historical practice and state racism. Forty of North Carolina’s 100 counties used to be covered by the preclearance provisions of Section 5 of the Voting Rights Act. “Preclearance” meant that those states and localities were not allowed to change their voting laws without proving to the Department of Justice or a three-judge federal court that the change would not make minority voters worse off. These were states with a history of racial discrimination in voting. But in 2013, in Shelby County v. Holder, the Supreme Court struck down Section 5, saying that preclearance was now unconstitutional because Congress did not base the list of states subject to precelearance on current voting conditions in the state.

[New evidence shows election officials are biased against Latino voters]

North Carolina passed its 2013 restrictive voting law just a month after Shelby. So is the change connected to is history of race discrimination? Real Clear Politics’ Sean Trende, testifying as an expert political analyst for North Carolina, noted that seven other states besides North Carolina had no same-day registration, no out-of-precinct voting, less than 17 days of early voting, no preregistration, and a photo ID requirement—all five changes that were being challenged. Many states lacked one, two or three of these voting rules. But only eight states lacked all five.  That testimony led to a very interesting exchange with ACLU lawyer Dale Ho, representing the plaintiffs, on cross-examination:

Ho: Could you read those eight states into the record, please?

Trende: Alabama, Michigan, Mississippi, North Carolina, South Carolina, Tennessee, Texas, and Virginia.

Ho:  Now, according to your opinion in this case, these eight states are in the mainstream; correct, Mr. Trende?

Trende: With respect to the voting practices at issue in this case, yes.

Ho: Now, it is true, is it not, Mr. Trende, that all eight of these states, with the exception of Tennessee, were at one point covered in whole or in part by Section 5 of the Voting Rights Act?

Trende: I do not know.

Ho of course was right that these seven were former preclearance states, suggesting that the vestiges of intentional racial discrimination still linger 50 years after the Voting Rights Act’s passage, something Trende did not factor into his analysis.

Political scientists are also weighing in on the last factor in Tokaji’s test: the nature of the state’s interest in these restrictive voting rules. So far political scientists have found very little voter fraud associated with practices such as same-day voter registration. An important study by Harvard’s Steve Ansolabehere and Stanford’s Nate Persily found no connection between a state having a restrictive voter identification law and voters’ confidence in the fairness of the electoral process.

Judge Schroeder could well be faced with a situation where plaintiffs have trouble proving the law will have a large discriminatory effect on African-American voters, but also ample evidence that North Carolina had no good antifraud reason or voter confidence reason for passing this law. The law was probably intended to help Republicans — who are overwhelmingly supported by white voters and not African-Americans in North Carolina — stay in office.

With this evidence and a murky legal standard, it is unclear what Judge Schroeder will do, but he was skeptical of plaintiffs’ case at an earlier stage of the case, denying a preliminary injunction against some of these practices.

Whatever Judge Schroeder decides, the North Carolina case could well end up before the Supreme Court. And if the history of the Supreme Court’s cases over 50 years of the Voting Rights Act is any guide, the fate of North Carolina’s law may depend less upon the political science evidence before the Court and more on the Justices’ ideological commitments and beliefs about the appropriate scope of voting protections for minorities.

Richard L. Hasen is Chancellor’s Professor of Law and Political Science at UC Irvine School of Law and author of the forthcoming book, “Plutocrats United: Campaign Money, the Supreme Court, and the Distortion of American Elections.”