If the Trump era has taught us anything, it's that large numbers of white people in the United States are motivated at least in part by racism in the voting booth. Donald Trump ran an openly racist campaign for president, calling Mexicans rapists and criminals, regularly retweeting white supremacists and at least initially balking at repudiating former Ku Klux Klan leader David Duke. Trump made it clear in his campaign that "Make America Great Again" meant that America was greater when white people's power was more sweeping and more secure. White voters approved of that message by a whopping 58 percent to 37 percent.

Trump made it clear in his campaign that "Make America Great Again" meant that America was greater when white people's power was more sweeping and more secure.

Some politicians deny the evidence, no doubt because they don't want to alienate white voters, including prejudiced ones. Other commentators try to parse whether Trump's racism will be a winning strategy in 2020. Terry Smith, a visiting professor at the University of Baltimore School of Law, offers a different response in his new book, "Whitelash: Unmasking White Grievance at the Ballot Box." Rather than excuse racist voters or try to figure out how to live with their choices, he argues that racist voting is not just immoral, but illegal. The government, Smith says, has the ability, and the responsibility, to address it.

This sounds radical. But Smith argues that it's in line with the Constitution and with years of court rulings. For example, Smith points out that racist appeals in union elections are illegal and that an election in which one side uses racist appeals can be invalidated by the National Labor Relations Board. Similarly, in the 2016 case Peña v. Rodriguez, the Supreme Court ruled that when a juror expresses overt bigotry, the jury's verdict should be invalidated.

"When voters go to the booth, they're not expressing a mere personal preference," Smith told me. According to Smith, voters who pull the levers to harm black people are violating the Constitution. If the Constitution means that overt racist appeals undermine the legality of union elections, it stands to reason that they undermine the legality of other elections, as well.

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So how can you tell when voters are acting out of prejudice? Again, Smith says, employment discrimination law provides a useful analogy. In discrimination cases, courts look for pretexts. If someone gives a reason for a hiring decision that is obviously false or makes little sense in context, the court has good reason to believe that prejudice or bias may have influenced the hiring decision.

Trump's unprecedented, compulsive, easily documented lying during the 2016 campaign made him an irrational choice. It's reasonable to conclude that voters were willing to swallow the falsehoods because they liked what they heard: overt racist appeals and incessant lies about rising crime rates. Research has since suggested that plenty of Trump voters were indeed strongly motivated by racist resentment and anti-immigrant animus.

Trump's unprecedented, compulsive, easily documented lying during the 2016 campaign made him an irrational choice.

The usual remedy for racial discrimination is censure or fines — as Trump was subjected to when the Justice Department found that his housing developments were discriminating against black tenants in the 1970s. It's more difficult to censure voters who have violated their constitutional duties. Nullifying elections would be essentially impossible. But Smith argues that there are other options.

"I think we can dismantle some of the features of the electoral system that encourage racialized decision-making," he says. "For instance, you only get a partisan gerrymander by moving people in and out of districts on the basis of their race." Ending this practice at the state and federal levels would be a big step toward reducing the power of racism at the ballot box, as would ending the use of Voter IDs intended to disenfranchise black voters.

Even more ambitiously, Smith suggests expanding the Voting Rights Act to address the racist patterns of voting in Senate elections in the South. Because the majority of white voters in the South vote Republican, and because they outnumber black voters, there isn't a single Democratic senator from the Deep South other than Doug Jones in Alabama, who may well lose his seat in 2020. Smith argues that we could remedy these disparate, racially motivated outcomes by creating Senate districts. Presumably, that would make it at least possible for black voters to elect a senator who would support their interests.

This is clearly a very controversial proposal, and its constitutionality has been debated in the past. But given obvious disparities in representation in the South, it seems worth considering again.

Over the last decade, an increasingly conservative Supreme Court has gutted the Voting Rights Act and upheld racist gerrymandering. Trump and Senate Majority Leader Mitch McConnell, R-Ky., are stacking both the Supreme Court and the federal courts more broadly with conservative judges. The prospect for an aggressive legislative response to racist voting seems slim.

Still, Smith points out, in the long term, "these remedies are a lot more practical than a lot of people might think." Republicans won't always control the presidency and the Senate, and judges don't live forever. Democrats could also expand the number of seats on lower courts or even on the Supreme Court — another controversial proposal known as court-packing. If Democrats decide that responding to racist voting is a vital priority, they could, in time, take steps to do something about it.

It's difficult to address injustice, however, if you're unwilling to say injustice exists. Politicians and pundits, Republican and Democratic alike, have been unwilling to reprimand voters or hold them accountable. But voters are not well-intentioned innocents who are helplessly manipulated by malevolent leaders. They make important decisions as constitutional actors, for which they have moral responsibility. Racist voting isn't an accident. It's a choice that may violate the principles of our Constitution and our legal system. We should say so, and then we should find ways to reduce the harm it causes.