On November 9, 2012, three days after Barack Obama’s re-election, the United States Supreme Court agreed to hear a landmark voting rights case. Four years on, we are about to find out just how far the conservative majority’s decision in Shelby County v Holder has tilted the playing field.

Shelby County, in Alabama, had a well-documented history of enacting regulations expressly designed to prevent blacks from voting, including poll taxes and literacy tests that whites were not required to take because of a so-called ‘grandfather clause’ exempting people whose forbears had voted before 1867.

For this reason, under Section Five of the Voting Rights Act, Shelby County was not allowed to make any changes to the way elections were conducted without checking them with the federal government first.

In all six southern states, plus Alaska, were prevented from making electoral changes. Shelby County’s lawyers argued that the Act’s list of places with egregious records of racial discrimination at the ballot box, drawn up at the height of the civil rights era, was out of date. Five of the nine justices agreed. “History did not end in 1965,” wrote Chief Justice John Roberts.

The Shelby decision gutted the Voting Rights Act, and so removed protections that had stood for half a century - preparing the ground for “the greatest attacks on voting rights since segregation,” in the words of Ben Jealous, President of the National Association for the Advancement of Coloured People (NAACP). Since the last presidential election, seventeen states have passed laws making it harder to vote, often with nakedly partisan intent.

Many of the laws passed by Republican-controlled state legislatures were modelled on a draft bill produced by a conservative think tank, the American Legislative Exchange Council (ALEC), requiring voters to produce photographic proof of identity from a narrow approved list skewed towards white voters.

The Heritage Foundation’s President, Jim DeMint, gave a candid assessment of the legislation’s impact. “It’s something we’re working on all over the country, because in the states where they do have voter ID laws you’ve seen, actually, elections begin to change towards more conservative candidates,” he said.

Under the Texas version, a concealed carry gun permit is an accepted form of identification, but a student identity card is not. The 600,000 or so Texans who lack passports or driving licences are disproportionately black and Latino. Many are among the state’s poorest citizens and cannot spare the time, effort and money required to get an identity card.

Striking the legislation down, federal Judge Nelva Gonzales Ramos wrote that it “not only had the effect of discriminating against minorities, but was designed to do so.” A conservative appeals court overruled her verdict on appeal.

The Governor of Texas, Greg Abbott, has claimed that the law is needed because “voter fraud is rampant,” but a study carried out by Justin Levitt, a professor at Loyola Law School, found only three documented instances of voter impersonation in Texas from 2000-2014, a period in which 72 million ballots were cast.

“Some politicians are looking at the nation’s voting laws and thinking ‘how can we get an electoral advantage?' Which is unfortunate, because you’re talking about people’s fundamental right to vote and it’s like a pawn on a chessboard, constantly being moved around,” says Ari Berman, author of a comprehensive history of voting rights in the USA, Give Us The Ballot.

In 2008, Barack Obama lost to John McCain among whites by twelve points, but still won because black, Hispanic and Asian voters turned out in record numbers. By contrast, in the 2014 midterm elections, turnout was the lowest since World War Two. The older, whiter electorate delivered a Republican landslide.

Paul Weyrich, one of ALEC’s founders, spoke openly about the importance of restricting access to the ballot box. “I don’t want everybody to vote… Our leverage in the elections quite candidly goes up as the voting population goes down,” he said. The Supreme Court’s Shelby ruling has vastly increased the scope for states to game the system.

Donald Trump will be the first presidential candidate to benefit. One quarter of eligible Americans - more than fifty million people - are not registered to vote. During the primaries, Trump talked about broadening the franchise. But when asked on MSNBC, he defended voter ID laws, saying: “I don’t think people should sneak in through the cracks.”

To cast her first vote, Jay Johnson had to pay a poll tax of $1.50. It was 1957, eight years before the Voting Rights Act made such levies illegal, along with literacy tests and other provisions crafted to exclude black voters.

For half a century, her home state, Virginia, was protected by Section Five of the Voting Rights Act. But soon after the Shelby ruling, its Republican lawmakers tightened Voter ID requirements. Now Johnson, a volunteer for Virginia Organizing, faces a battle to register and educate voters, to minimise the impact of the law.

Many of the older men and women that she meets in rural areas don’t have birth certificates. An estimated 200,000 Virginians lack a driving licence. The law is not as strict as in Texas - student IDs are valid and free identity cards are much easier to get - but Johnson has observed a deterrent effect.

“If you feel left out of the process, everything that’s put in your way becomes one more hurdle, and after a while you get tired and discouraged. And that’s really what the opposition is counting on when they put in these laws,” she says. “The more you discourage people, the more you can control the system.”

Political scientists at the University of California compared turnout in states that did and did not have voter ID laws for elections between 2008 and 2012. They found "substantial drops in turnout for minorities under strict voter ID laws” - more than 10% for Hispanics and almost 13% for mixed race voters.

“A little bureaucracy goes a long way, unfortunately,” says Julie Eberstein, an American Civil Liberties Union (ACLU) attorney. “People have to take time off work on a weekday. Things that seem like a little bureaucracy to us may be really prohibitive for… low literacy voters, homeless voters, other voters who don’t have the capacity to overcome these hurdles.”

In May, a federal judge, Henry ‘Hang ‘Em High’ Hudson, rejected a legal challenge to Virginia’s voter ID law. Although the state did not present a single case of voter impersonation, he found that “the statute’s stated intention of protecting the integrity and reliability of the electoral process serves a substantial governmental interest.”

He noted that “Virginia has an unfortunate history of racial discrimination and statutory artifice to hinder black voting,” but disagreed with the Democratic plaintiffs that the voter ID law was a deliberate attempt to disenfranchise African-Americans.

“It can be very difficult to show intent, but… I would not be surprised if legislators passed this in full knowledge of how many people don’t have ID,” says Eberstein. In a similar case in Wisconsin, a court heard that Republican state representatives were “giddy” about the prospect of driving down turnout in African-American neighbourhoods and college towns.

In April, Virginia’s Democratic Governor, Terry McAuliffe restored the voting rights of ex-felons. Previously, more than 200,000 people with a criminal record were deprived of their vote, and could only get it back ten years after serving their punishment by filling in a thirteen page form and supplying all relevant court documents. A disproportionate number of convicted felons are from the black community.

The Sentencing Project estimates that 5.85 million Americans cannot vote because they have been convicted of a crime. This includes prisoners, people on parole or probation, and former felons in states that strip disenfranchise criminals.

“In Fredericksburg, it’s not that hard to end up with a felony,” says Odessa Hudson. She was twenty-three years old, pregnant and estranged from her family when cops burst in to her motel room and accused her of selling drugs. They found a small bag of crack cocaine in a tissue box - Hudson believes it was planted by a woman with a grudge against her - and charged her with possession with intent to distribute.

Facing twenty years in prison, she took a plea deal. The charge was downgraded to possession and she received a five year suspended sentence and six months house arrest. She also lost her right to vote. It would be two decades before she got it back.

Hudson now has four children. She spends what little free time she has registering people to vote. “There’s people from my community that went to jail for one thing or another and I know that they’re home and it’s been years, and I’ll go seek them out and tell them the good news. I’m like the Mormons or the Jehovah’s Witnesses,” she laughs.

More than half of Virginia’s ex-felons are African-American, a group that overwhelmingly votes Democrat. “It is hard to describe how transparent the Governor’s motives are,” said Bill Howell, the Republican Speaker of Virginia’s House of Delegates. “The singular purpose of Terry McAuliffe’s governorship is to elect Hillary Clinton President of the United States.”

As McAuliffe used to be Clinton’s campaign manager, this was a fair point. But restoring the vote to ex-felons also rights an appalling injustice. Virginia’s 1902 constitutional convention disenfranchised criminals for the same reason it required prospective voters to pay a poll tax and pass a literacy test: to exclude freed slaves and their descendants from the political process.

“I told the people of my county before they sent me here that I intended, as far as in me lay, to disenfranchise every negro that I could disenfranchise under the Constitution of the United States, and as few white people as possible,” delegate R.L. Gordon told the convention.

On July 19, Virginia’s Supreme Court will hear a Republican challenge to McAuliffe’s executive order. As Barack Obama’s margin of victory in Virginia was fewer than 150,000 votes last time around, the outcome of the case could prove decisive this November.

Across the USA, the election is already being fought in the courts, in lawsuits challenging voting restrictions. In Ohio, for instance, the ACLU is suing Secretary of State Jon Husted for purging almost two million voters from the rolls. Voter ID in Texas and Wisconsin is probably headed to the Supreme Court.

It is likely to be one of the dirtiest presidential elections ever, not merely in the muck-raking, insult-trading sense, nor even the volume of anonymously-funded attack ads. Anything that gets the right people to the polls and shuts the wrong people out is fair game.

In Maricopa County, Arizona - a jurisdiction formerly subject to pre-clearance under the Voting Rights Act - some voters in the primary elections this March had to queue for five hours, after officials eliminated 70% of the polling stations, ostensibly to save money.

There are certain to be long queues on election day. In 2012, the last ballot in Florida was cast at two in the morning, well after Mitt Romney had conceded defeat. Ohio’s Republicans recently passed a bill requiring voters to pay a five figure cash bond to keep polling stations open late in the event of delays.

In the face of such determined efforts to deter people, all voting rights activists have is the power of persuasion. “In my experience, there are people who have had their votes taken for so long, they’re disinterested,” Odessa Hudson says. “But I’m gonna knock on as many doors as I can.”