Voting rights groups are struggling to hold back a tide of new laws that are likely to make it harder for millions of Americans to vote in the presidential election in November and could distort the outcome of the race for the White House.

Since January 2011, 19 states have passed a total of 24 laws that create hurdles between voters and the ballot box. Some states are newly requiring people to show government-issued photo cards at polling stations. Others have whittled down early voting hours, imposed restrictions on registration of new voters, banned people with criminal records from voting or attempted to purge eligible voters from the electoral roll.

The assault on voter rights is particularly acute in key swing states where the presidential race is likely to be settled. Five of the nine key battleground states identified by the Republican strategist Karl Rove have introduced laws that could suppress turnout – Florida, Iowa, New Hampshire, Ohio and Virginia.

Between them, the states that have imposed restrictions account for the lion's share of the 270 electoral college votes that Barack Obama or Mitt Romney must win to take the presidency. Sixteen of the states that have passed new voter restrictions between them hold 214 electoral votes.

"We are seeing a dramatic assault on voting rights, the most significant pushback on democratic participation that we've seen in decades," said Wendy Weiser of the non-partisan thinktank the Brennan Center for Justice, and the co-author of the definitive study of US voter suppression in the 2012 election cycle. "These laws could make it harder for millions of eligible American citizens to participate, particularly in swing states."

The epicentre of the attack sweeping across America is Florida, which has a long history of voter suppression. With a famously evenly balanced population that in 2000 elected George Bush by an official majority of only 537 out of almost 6 million votes cast, even relatively minor distortion of electoral turnout could have huge implications not just for the result in Florida but, given the state's prominent role in determining the outcome of recent presidential elections, the whole of the US, and – by extension – the world.

Florida Republicans have made several blatant attempts to suppress turnout this election cycle. One of the first acts of governor Rick Scott when he took office in 2011 was to reimpose what is in effect a lifelong voting ban on anyone convicted of a felony - including 1.3 million Floridians who have fully completed their sentences.

"There are over a million people in Florida who no longer have the full rights of citizenship and right to vote," said Baylor Johnson of Florida ACLU. "One million people – that's the White House for a generation, which gives you an idea of why they are trying so hard to stop people voting."

The felony trap is just a small part of it. Over the past 18 months the Republican-controlled state government in Florida has introduced a rash of new restrictions. They include a reduction in early voting hours that will hit black communities that made disproportionate use of the opportunity through their churches; changes to the rules that will make it harder for those who change address to vote and could catch hundreds of thousands of families who have lost their homes through foreclosure; and attempts to erase thousands of voters from the electoral roll through a "purge list" that was so flawed that the state's electoral supervisors refused to touch it.

"Florida has proven to be a testing ground for voter suppression techniques across the country. It's ground zero of this stuff," said Hilary Shelton who heads the NAACP's Washington bureau.

Republican lawmakers in Florida and the other 18 states that have gone down the road of voter restrictions this election cycle insist they are motivated by a concern to prevent fraud. When the governor of Texas, Rick Perry, introduced a voter ID law last year he did so using his emergency powers, saying the rule change would "appropriately help maintain the integrity and fairness of our electoral system".

Yet studies into the extent of fraud at the polls have found cases few and far between. "You are more likely to find someone struck by lightning than someone who carries out impersonation fraud to cast an improper vote," Weiser said.

Occasionally the veil has slipped, revealing what might be a deeper motivation for Republican lawmakers. Last month, Mike Turzai, leader of the Republicans in the Pennsylvania assembly, addressed a rally of party members about the state's new voter ID law that could ensnare more than 750,000 registered voters who do not possess the necessary photo cards recognised under the new rules.

"Voter ID, which is going to allow Governor Romney to win the state of Pennsylvania. Done," said Turzai.

'I don't have a problem making it harder'

A leading New Hampshire Republican, William O'Brien, speaking to the party faithful earlier this year at a time he was attempting to pass a law that would have prevented many college students voting in the state, gave an inkling of his thinking. Students were "foolish," he said. "Voting as a liberal. That's what kids do … they just vote their feelings."

True to form, it was a Florida Republican, Mike Bennett, who put it most succinctly, saying during a debate about the state's voter clampdown that he wanted to make democratic participation easy. "I don't have a problem making it harder. I want people in Florida to want to vote as bad as that person in Africa who walks 200 miles across the desert. This should not be easy."

Not all the steps taken to turn the November presidential election into a walk across the Saharan desert are as comical as Georgia's. As the Jackson Free Press discovered, under the state's new rules, voters would need to produce a certified birth certificate in order to get a photo ID, but would need to produce a photo ID in order to get a certified birth certificate.

Georgia's catch-22 is currently on hold pending federal approval for its voter ID law. The US department of justice has been taking a robust stance this year, blocking attempts to suppress the turnout in Texas and South Carolina, while civil lawsuits are pending in Pennsylvania and several other states.

But with the presidential election less than four months away, electoral observers are watching closely to monitor the effects of restrictions that almost invariably hit poor people, black and other ethnic minorities, elderly people and students. The added burden falls in a variety of ways: poor people, for instance, often do not have cars, and so find the trip to an office issuing ID cards more onerous. African American men have higher rates of felony convictions and therefore fall into the felony trap – in Florida about one in five black men have been disenfranchised effectively for life.

For observers of Florida's long history of electoral discimination, this all sounds far too familiar for comfort. Before the 1965 Voting Rights Act, Florida, mirrored by others across the south, deployed a number of techniques to prevent black people voting.

There was the poll tax that allowed everybody to vote, as long as they could afford the tax (many African Americans couldn't); a literacy test that allowed whites to vote with a simple cross while blacks had to recite the preamble to the constitution word perfect before they could cast their ballot; and "multiple annexations", where voters had to travel to several offices over distances of 100 miles or more just to ensure they could vote.

Such egregious barriers are in the past, but the rash of new laws erecting hurdles in the 2012 election cycle has chilling echoes. "We are looking at a return of discriminatory policies at state level," the NAACP's Shelton said. "Jim Crow might be dead and buried, but James E Crow Esq. is very much alive and kicking."

© Guardian News and Media 2012