In a park near Little Havana in Miami yesterday, a politician with a boyish grin named Marco Rubio, whose parents arrived from Cuba five decades ago, jabbed his pen at a sheet of paper to whoops from the small crowd.

The gesture was small, and apparently unassuming, but its consequences could be great. And for another politician – one not present in that park – the stroke of Rubio's pen might as well have been a hammer driving nails into his palms.

That politician is Charlie Crist, the Governor of Florida, who until a year ago was one of the most popular and beloved figures in the Republican Party. A moderate, he was seen by many as a possible vice-presidential candidate in 2008. Since then, he has been strung up in a political crucifixion about as swift and cruel as any you are likely to see in America.

Rubio, a former Speaker of the Florida legislature, is the man responsible, though Crist has performed a little self-flagellation of late. The rally in the park, attended by members of Rubio's family and 100-odd supporters, was the moment the 38-year-old Cuban-American, hailed by some on the right as their answer to Barack Obama, signed the papers qualifying him to take on Crist in the primary elections to determine who will compete for the Republicans for an open seat in the US Senate.

That someone as tender, and ideologically far, from the party mainstream could end up being a threat to Crist's ambitions to transition from the governorship to become one of Florida's two US senators would have been unthinkable until not long ago. Rubio, for example, is the man who at a recent conservative gathering in Washington declared his love for Guantanamo and his support for a form of torture known as water-boarding.

But he is much more than a threat now. With demigod status in the ranks of the Tea Party protest movement, Rubio would almost certainly crush Crist when Florida Republicans vote for their nominee in August. A recent Rasmussen poll saw Crist with 28 per cent support versus 57 per cent for the former Speaker.

Not accustomed to being political toast, Crist faces a stark choice. The GOP's rules say he must decide this week whether to drop out altogether, stick with it, or seize at the only other realistic option open to him: cut loose from the party he has served all his political life and run for the Senate as an independent. The Governor told members of his cabinet yesterday to expect a public decision tomorrow.

This is much more than a local squall. Political dramas in Florida always bring national reverberations because of the pivotal part the state plays in every presidential contest. Now the state has set itself up as the ground zero for what may be the most important political upheaval seen in America in a generation: the resurgence of right-wing, conservative zealots whose creed is small government, low taxation and zero bi-partisan cooperation.

It is a phenomenon that has been manifested, in part, by the so-called Tea Party. Its sudden sprouting across the political landscape – a Gallup poll yesterday showed 28 per cent of Americans voicing support for it – has clearly sent a chill wind through the Democratic Party. But it is also threatening to tear apart the Republican Party, undoing Ronald Reagan's notion of a "Big Tent" party open to all shades of conservatism and erecting instead an edifice narrowly reserved for purists.

This is what Jim DeMint, a Republican Senator from South Carolina and vocal Rubio fan, meant when he said a few months back: "I would rather have 30 Republicans in the Senate who believe in principles of limited government, free markets, free people, than to have 60 that don't have a set of beliefs."

Among those Republican figureheads who have endorsed Rubio and tipped Crist into the drink are the likes of Dick Cheney and Rudy Giuliani. Giuliani has never forgiven Crist for endorsing John McCain over him in 2008 for the presidential nomination. Last week former Massachusetts Governor and presidential hopeful Mitt Romney also climbed aboard with Rubio, even though he himself was once the definition of a big tent Republican. Not even McCain is standing by Crist, running for cover this week unable to find it in himself to say anything positive about his old friend. As for the idea that the Florida Governor could run as an independent for the US Senate, McCain told a reporter: "I support Republicans."

The Republicans, Dana Milbank of the Washington Post argued, "are in a dogmatic race to the bottom as they drop Crist for his far-right challenger". What has the man done to deserve so sharp a cold shoulder from old friends? Even the National Republican Senatorial Committee, responsible for winning as many Senate seats as possible for the party, told Crist to get out of the way.

The simple answer is not unrelated to a road-building ceremony attended by Crist this Monday. It will be funded partly by President Obama's $787bn stimulus programme. Conservatives despise the stimulus dole-out. To them it symbolises big-spending and deficit growth. Not only did Crist accept the money (in common with almost every other governor) but when Obama came to Florida last year for a public rally in Fort Myers, Crist – for a split second – embraced him. It was a moment they called the "hug" and it has been damaging him since.

The Crist hug has entered popular US political lore alongside the Lieberman kiss. Joe Lieberman did, in fact, attain the heights of running for vice-president. Yet he was effectively expelled from the Democratic Party because of a similar moment in 2005 on the floor of the US Congress – a momentary chest-bump with George W Bush. The moment set off a bomb under Lieberman who had already earned the disdain of many Democrats for supporting the invasion of Iraq. Lieberman responded by leaving his party and winning in Connecticut as an independent.

But even moderate Republicans have had reason of late to feel dismayed by Crist recently. The Governor seemed to abandon his own convictions earlier this spring, for instance, when he vetoed a bill passed by the state legislature linking teachers' pay to the achievements of students. The law had strong support from the Republican mainstream in Florida, not least from Crist's predecessor, Jeb Bush.

But the disdain in which he is held by riled-up conservatives is not altogether reasoned. Crist is pro-gun, anti-gay rights and anti-abortion and has regularly paid lip service to the cause of small government. Unconvinced hardliners point instead to Crist's bipartisan tendencies. "There are people," Rubio recently averred, "who believe the way to be more successful as Republicans is to be more like Democrats. And the people who believe we need to be more like Democrats will vote for Charlie Crist."

Adding to the frustration of Crist and his dwindling band of allies are polls showing that, when it comes to the general election in November, he would beat the likely Democratic nominee, Congressman Kendrick Meek, just as Rubio would. But it is another poll, by Quinnipiac University in New York, that was surely getting the Governor's attention yesterday. It suggested that were he to run as an independent he would beat both Rubio and Meek in what would, at that point, become a three-way race in November.

But several obstacles have come into view. As a Republican, Crist still has access to the bank accounts of many rich supporters. Cutting loose from the Republicans would narrow his access to the considerable sums of money needed to stage a credible campaign. Plus he would not have the party – the senatorial committee in Washington – gunning for him with all it can provide; money, endorsements and advertising. Yet, there are few political observers left who do not believe that, by tomorrow night, Crist will have bolted the party of Reagan and Bush and set up shop on his own. "The clock is making him decide now. I just don't see a path for him to stay in the Republican primary," David Johnson, a Republican consultant, said.

An independent run by Crist would at least provide a litmus test of where the party, and even the country, may be headed. When all the Tea Party noise is left outside and Florida Republicans find themselves alone in the booth, what kind of politician will they ultimately choose to serve them in Washington? The pragmatist or the ideologue?

Leading Independent Politicians

Bernie Sanders

In a country where socialism is a dirty word, Bernie Sanders is the rarest of exceptions: an avowed critic of American capitalism who manages to hold on to a Senate seat with a vast majority and little complaint from either Republicans or Democrats. Sanders represents Vermont, a state whose maverick streak is emphasised by a healthy secessionist movement. Always an independent, he first won election to the House of Representatives in 1991, and was elected as the state's Senator in 2006. Much loved by his constituents, he initially alienated Democrats by painting them as indistinguishable from their Republican opponents – but the workoholic gradually earned their respect over his long career. "I'm not afraid of being called a troublemaker," Sanders once said. "But you have to be smart. And being smart means not creating needless enemies for yourself."

Joe Lieberman

In 2004, Joe Lieberman was the Democratic candidate for vice- president; now he is an independent senator, loathed by many in his former party, and refuses to rule out running as a Republican in the next election. Lieberman, who represents Connecticut, first split from the party when he was defeated in the primary by an anti-war candidate who took advantage of anger at his support for the invasion of Iraq – but ran anyway as an independent in the general election, and won. Since then he has infuriated his former party by supporting John McCain in the 2008 presidential election, and delaying and diluting healthcare reform proposals. Those moves have dismayed his former supporters in Connecticut, too, and he may face a tough challenge to retain his seat when it comes up for re-election in 2012.

Michael Bloomberg

A lifelong Democrat, Bloomberg, the 8th richest man in America, changed his affiliation to the Republican Party so he could run on their ticket for mayor of New York. He duly won, but in 2007 dropped his party affiliation to become an independent, saying that the change had brought his official position "into alignment with how I have led and will continue to lead our city". While the move made little difference to his status in New York – where his huge wealth means that he has never needed to kowtow to the party political interests that affect most politicians – it did increase speculation that he was planning a run as an independent presidential candidate in 2008. After a lengthy period of indecision, he decided not to run in February that year. Speculation continues that he could revive his presidential campaign for another shot at the office in 2012.

Jim Jeffords

Like Sanders, Jim Jeffords was a senator from Vermont; very much unlike Sanders, he was a Republican. When he first entered the Senate, in 1988, he was a loyal party member, albeit firmly on the moderate wing. But as the party moved further right, he became alienated. In 2001, the Senate leadership refused to sanction funding for a bill that would place disabled children in mainstream schools, and Jeffords decided he had had enough. Becoming an independent earned him the fury of former colleagues. But, he wrote in his autobiography, "I had to be true to what I thought was right, and leave the consequences to sort themselves out." He retired in 2006, continuing to vote with his former party on many issues but voting against the war in Iraq. Only one Republican applauded his final speech.