The fewer people vote, the greater the Republican Party’s chances of winning. The higher the turnout, the better for the Democratic Party. Democrats have won the popular vote in five of the last six presidential elections by motivating young people, blacks and Latinos to show up in record numbers. If they can do so again, Hillary Clinton’s victory is assured.

Republicans have been quite candid about this. "If we do not suppress the Detroit vote, we're going to have a hard time in this election cycle,” former Republican state representative John Pappageorge said, and one senior official with the Trump campaign even boasted “we have three major voter suppression operations under way,” to discourage Bernie Sanders supporters, young women and African-Americans from casting a ballot.

Many of the most consequential battles of this presidential election have already been fought, as the Grand Old Party seeks to restrict the franchise any way it can and Democrats fight to expand it.

In Ohio, a federal appeals court prevented Secretary of State John Husted from purging tens of thousands of voters from the rolls. In Virginia, Democratic Governor Terry McAuliffe restored the voting rights of 200,000 people with a criminal record, only for the state’s Supreme Court to take them away again.

Courts weakened discriminatory Voter ID laws in Texas and Wisconsin, but in several Texas counties, signs falsely stating that a photo ID is required to vote have not been taken down. Wisconsin’s lawmakers commissioned a short film explaining that a birth certificate is no longer needed to register, but didn’t show it at cinemas in Milwaukee, where most of the state’s black voters live.

Millions of US citizens don't have the forms of ID these laws require - with many poor and from a minority background voter ID laws tend to suppress voter turnout among people who tend to vote for the Democrats.

After a court ruled that North Carolina counties must keep “at least one” polling station open throughout the two week early voting period, several Republican-controlled counties did literally that. In the last presidential election, Guilford County, home to half a million people, set up sixteen sites for early voting: this year it provided one. In Craven County, the queue to vote was two hours long.

Dirty tricks peak in the week before Election Day. In 2004, flyers were distributed in Milwaukee’s African-American neighbourhoods telling residents that if they had received so much as a parking ticket, they were no longer eligible to vote. In 2008, flyers in Virginia claimed that "due to larger than expected voter turnout in this year’s electoral process,” Republicans should vote on Tuesday and Democrats on Wednesday.

Last month, voters in the Republican-leaning suburbs of Albuquerque, New Mexico, received leaflets telling them: “When the Democrats win the election and you didn’t do your part… your neighbours will know… after all, voting is a matter of public record.” An aerial shot of houses showed some with red ticks and others without.

Such tactics border on illegal, but the culprits are rarely prosecuted. Harassing robo-calls in the middle of the night, police speed traps outside polling stations, threatening billboards warning that casting a fraudulent vote is a crime: in the United States this is known as “political hardball”. It is just how the game is played.

The difference this year is that one of the nominees, Donald Trump, is openly calling for his supporters to intimidate voters in “other communities” on election day.

“To encourage people to watch polling places for possible criminality when one of the candidates has already said, as fact, that there is going to be rigging going on, it sounds like a recipe for something: disaster maybe, conflict probably, certainly heightened tensions,” says Ryan Lenz, of the Southern Poverty Law Centre, which monitors hate groups in the USA.

“There has been so much talk about potential efforts to intimidate or harass voters at this election,” says Brenda Wright, Vice-President of Legal at Demos Action. “We are all hoping that that talk turns out to be a lot more bark than bite, and that we’re not really going to be seeing people roaming polling places with guns and video cameras.”

In 1981, Republican Thomas Kean narrowly defeated Democrat James Florio to be elected Governor of New Jersey. Afterwards, Democrats sued, claiming that off-duty cops and deputy sheriffs hired by the Republican party had “obstructed and interfered” with the election process. Signs outside polling stations in black neighbourhoods read: "This area is being patrolled by the National Ballot Security Task Force.”

Rather than contest the lawsuit, the Republican National Committee agreed to a consent decree, banning it from engaging in any such “ballot security” efforts. The decree has since been broken, renewed and modified, and is still in place. This week, the Democratic National Committee sued again, claiming the GOP has colluded with and tacitly condoned Trump’s efforts to “intimidate and discourage minority voters”.

This will not be easy to prove, as the most organised efforts to challenge the validity of Democratic votes on the pretext of cracking down on voter fraud are being carried out by third party groups officially unaffiliated with the Trump campaign.

True The Vote grew out of a Texan Tea Party chapter called the King Street Patriots. Tom Fritton of Judicial Watch is a regular speaker at the group’s events, where he warns that a “food stamp army” is being raised by Democrats, to steal the election with the help of the “illegal alien vote”.

“Democrats are very good at getting the discussion about voter suppression going right before an election, and it’s not so much a discussion about civil rights - it’s more about exciting the base,” says True The Vote spokesperson Logan Churchwell. “Republicans have not done that kind of tactic until Donald Trump came along and started talking about election rigging and saying ‘you gotta go poll watch.’ He’s trying to excite his base the same way Democrats do.”

True The Vote trains poll watchers how to challenge voters seeking to cast a ballot and provides the connections they need to be accredited as an observer by the local Republican party. Logan says that this year, the group has been training 200-250 people a day and setting them up with a mobile app to report possible instances of fraud.

Forty-six states allow poll watchers to challenge a voter’s eligibility: some inside the polling station, some outside; some in writing, some in person. Federal law 18 US Code Section 594 decrees that any activity that “intimidates, threatens, coerces” voters constitutes intimidation and is punishable by up to a year in prison, but it is far from clear how aggressive a challenge needs to be to cross the line.

Trump confidant Roger Stone says he is sending more than two thousand “volunteer exit pollers” into “certain targeted precincts, in certain targeted counties, in certain targeted states, where we think they may steal,” namely Cleveland, Detroit, Philadelphia, Las Vegas, Milwaukee, Fort Lauderdale, Charlotte, Richmond and Fayetteville: the cities with the biggest minority populations in swing states.

On Wednesday, Stewart Rhodes, the leader of the Oath Keepers, one of the largest and most influential anti-government groups in the country, posted a message online, announcing Operation Sabot 2016: “[W]e call on you to form up incognito intelligence gathering and crime spotting teams. And go out into public on election day… with video, still camera, and notepad in hand, to look for and document suspected criminal vote fraud or intimidation activities.”

Last year, the Oath Keepers made international headlines by showing up at the anti-police brutality protests in Ferguson, Missouri, toting semi-automatic weapons, supposedly to keep the peace. Incognito is not their style.

“Wherever you see the Oath Keepers, you see a hefty collection of AR-15s,” says Lenz. “It’s not really their MO to blend in with the population but that’s exactly what Stewart Rhodes has encouraged them to do, which is doubly concerning. Will they be carrying concealed weapons? They might not be carrying an AR-15 but will they have Glock 40s tucked in their waistbands?”

In previous general elections, the federal government dispatched trained election observers to counties with a record of racial discrimination at the polls. As a result of the Supreme Court’s decision gutting the Voting Rights Act, in 2013, it has drastically cut back on this programme, and will send hundreds rather than thousands of observers, to stand outside rather than inside polling stations.

“The loss of the federal observer programme this election cycle is significant,” says Kristen Clarke, President of the Lawyers’ Committee for Civil Rights Under Law. “There are parts of the country where we have seen a history of eleventh-hour vote suppression efforts, and federal observers played an important role in deterring mischief and ensuring the fair treatment of voters.”

The Election Protection Coalition has set up a hotline, 866-OUR-VOTE for people to report obstruction or interference, and has a team of lawyers on standby to file lawsuits (to keep polling stations open if there are long delays, for instance) but much of the work of protecting voters will be done on an ad-hoc basis by volunteers.

“On the street it’s a different play,” says Philadelphia’s former city manager Joe Certaine. “Bringing people from outside of Philadelphia to monitor polling places in African-American wards may be illegal, but the legalities have got to be sorted out by attorneys in courts of law and by then it’s too late… If there is a threat, if there’s intimidation or harassment, it will be met with a defence of those voters.”

Challenges are unlikely to turn up much in-person voter fraud, as study after study has shown it to be vanishingly rare, but they are certain to gum up the works and make it harder and more stressful to vote. Long queues on election day are inevitable, particularly in Republican-controlled counties that have cut the number of polling stations, ostensibly to save money. In Maricopa County, Arizona, people waited five hours to cast a ballot in this year’s primary.

For everyone committed to ensuring the integrity of the USA’s elections, on right and left, November 8 will be a long day. “It is a little bit like running around putting out fires, unfortunately,” says Walsh. “We just hope that there are not too many fires.”