For someone who holds the relatively modest position of county sheriff, Joe Arpaio has received an astonishing amount of attention from this year's Republican presidential candidates.

He has been wooed by Michele Bachmann, Herman Cain and Rick Santorum, who all made pilgrimages to Arizona to see him in person, Santorum as recently as last week. Rick Perry invited him to tour Texas with him and Mitt Romney, for whom he acted as Arizona campaign chair in 2008, has also been in contact.

There is a simple reason for this otherwise peculiar courting of an ageing and famously grouchy middle-ranking official: the area that Arpaio polices around Phoenix, Arizona's capital, is the ground zero of the fight against illegal immigration in America and he is its most famous advocate.

For two decades, he has studiously cultivated his image as "America's toughest sheriff" – raiding private businesses suspected of employing undocumented workers, rounding up Latinos as they are smuggled across the border with Mexico, sending his "posse" to swamp entire neighbourhoods and arrest individuals, usually Hispanic, for often minor infringements, handing anyone found to be undocumented to the Feds.

"They say I racially profile," Arpaio said in his office in downtown Phoenix on the eve of Arizona's Republican primary on Tuesday. "But we arrest everybody – it's not my fault a high percentage happen to be here illegally."

In the past two years, Arpaio's once lonely stance as the tough guy of US immigration policy has suddenly become de rigueur on the American right, inspired by the rise of the Tea Party movement. His approach has been elevated into Arizona state law, in the form of SB 1070, a crackdown on undocumented Hispanics that requires police to check the papers of anyone they suspect of being unlawfully present.

SB 1070 has spread like wildfire to other states across America, from Alabama and Georgia to Oklahoma and Missouri and many more.

Hence the unseemly rush of presidential candidates seeking Arpaio's endorsement. Both frontrunners, Romney and Santorum, who are locked in a bitter battle for the Republican nomination, have embraced Arizona's example.

Last week, Romney went so far as to laud SB 1070 as a model for America. On Sunday Jan Brewer, the Arizona Governor, returned the favour by endorsing Romney.

"He has that pro-business background and he has that political history that I think ... would serve America the best," she told NBC's Meet the Press. "I think he is the man who can carry the day."

But there are storm clouds gathering over Arpaio that should give Romney and Santorum pause. The sheriff is under investigation from the US justice department for racial profiling of Hispanics. He also faces growing opposition from a nascent Hispanic electorate that is finally discovering its voice.

A coalition of Hispanic and labour organisations in Arizona has just launched a campaign to oust Arpaio, who comes up for re-election in November. Led by Citizens for a Better Arizona, it produced a TV advertisement accusing the sheriff of wasting $50m (£31m) of taxpayers' money which aired during last week's Republican debate.

Arpaio says he is utterly unflustered by the opposition. "They are going after me, hoping I retire or get defeated. But I've got news for them: I'm not going anywhere."

Russell Pearce did not think he was going anywhere either. As leader of the controlling Republican group in the Arizona state senate, he was the architect of SB 1070. His aim in framing the bill was to drive illegal immigrants out of Arizona. As he puts it when we meet in a cafe in a Phoenix suburb: "Illegals are criminals, they come across the border because we incentivise them with jobs and free stuff. Lots of free stuff. We fertilise our weeds in society today."

Pearce is proud of the fact that more than 100,000 undocumented immigrants have already fled Arizona under the shadow of SB 1070 – and that is before the supreme court rules this summer on the new law. If the court allows key provisions to stand, another mass exodus could follow.

Pearce has one other statistic of which he is very proud: so many children have been taken out of schools in his district because of the fears of their undocumented, primarily Hispanic, parents that the authorities could close 13 elementary schools and save the taxpayer $400m.

Despite such success, as he sees it, Pearce has paid a heavy personal price for spearheading the crackdown. The same coalition that is turning its sights on Arpaio forced a recall election against him last November, which he lost. Since then he has been in the political wilderness.

Like Arpaio, Pearce is dismissive of the opposition that ousted him. "This recall was brought on by far-left folks, the open-border crowd, anarchists. I wouldn't disrespect the name communist by calling them that."

He has vowed to continue his mission to drive all undocumented families out of Arizona and is considering standing for office again this November, all of which delights Randy Parraz, the community organiser who led the recall campaign that drove Pearce from power.

"Pearce is still in denial and that's great because if he tries to make a comeback we will do the same to him again," Parraz said.

Parraz believes that Pearce and Arpaio – and, by extension, the Republican presidential candidates who are so eager to embrace them – are making a huge political mistake. "They don't realise that there are consequences to their extreme and arrogant behaviour: they are going to drive the Latino voters to the polls like nothing else."

Parraz goes so far as to venture that Arizona – a state that has voted Republican in every presidential election since 1952 other than Bill Clinton's victory in 1996 – could turn permanently Democratic as a result of the Republican party's perceived hostility towards Hispanics.

"It's not a matter of if Arizona will go blue [Democratic], but when," he says.

An army of volunteers is working quietly in Arizona to increase Hispanic voter registration and participation before the November presidential election. A fifth of the state's eligible voters are now Hispanic, yet just 43% of them cast their ballot in 2010 – 15% below the proportion of the general population that voted.

If that democratic deficit can be closed, it could have a huge political impact. Francisco Heredia of Mi Familia Vota, a group that encourages Hispanics to vote, aims to persuade 50,000 Latinos to register to cast their choice early by mail in the presidential election, as that will give more time for canvassers to ensure they participate and could, he believes, raise turnout to 65%.

The same push to get out the vote is under way in key battleground states with large Hispanic populations across America, raising the prospect that the Latino vote could determine the outcome of the presidential election itself.

Jeb Bush, brother of George and the former governor of Florida, has predicted that Hispanics will control the margin of victory in 15 states which will decide who takes the White House.

Yet the Republican grip on Hispanic voters is slipping. In 2004, George Bush gained 44% of the Hispanic vote and held on to the presidency; in 2008 John McCain gained only 31%. This year, that figure could fall further as a result of the Republicans' aggressive posture on immigration.

Demographically, Latinos are the voting group to watch. The number of eligible Hispanic voters has increased from 13m in 2000 to 21m in 2010 – a rise that is particularly evident in battleground states such as Arizona, Nevada, New Mexico, Florida, Pennsylvania and Virginia. In Nevada and Virginia, the Latino population has nearly doubled in the past decade.

Take a long view and the picture is even clearer: nearly a quarter of all children in America are Latino and, according to the Pew Hispanic Centre, every year about 600,000 US-born Latinos turn 18 and become eligible to vote – a demographic timebomb that should be focusing the minds of every American politician.

It is indeed focusing the mind of Barack Obama. He is regularly to be heard addressing Spanish-language media and his re-election campaign is openly courting Hispanic voters in all relevant battleground states.

Meanwhile, the Republican presidential nominees are paying homage to Arpaio.

In the view of the sheriff's arch-nemesis, that is political suicide. "The Republican anti-Latino platform is going to lock the Latino vote into the Democratic camp for a generation," Parraz says. "In order to placate the Tea Party, they are going to pay a terrible long-term price. To which I say: 'Hallelujah brother! Keep on doing that!'"