It is the rumour that – almost – dare not speak its name.

But, as the Republican nomination race descends into civil war in Florida, some senior figures on the right of American politics are speculating openly about the prospect that none of the contenders should win.

Instead, they argue, several scenarios could play out which would allow someone not currently in the race to step in at the last moment, or appear at the party's convention in Tampa in August, and win the right to fight Barack Obama for the White House.

That is possible because in the American system a party's nominee is chosen by delegates, which are won via the primary and caucus states who then send them to the convention to vote for their particular candidate. Thus, in order to become the nominee, a candidate must amass a total of 1,144 delegates to take to Tampa. So far, with only three small states having already voted, that contest has barely begun.

The current favourite choice to jump into the race, bolstered by his performance delivering the Republican rebuttal to Obama's state of the union speech, is Indiana governor Mitch Daniels. But a familiar roster of other names are also floating around Republican circles, such as New Jersey governor Chris Christie, Wisconsin congressman Paul Ryan, former Florida governor Jeb Bush or current Florida senator and Tea Party favourite Marco Rubio.

The problem is simple. Former speaker Newt Gingrich is seen by many Republican insiders as too volatile and having too much historical baggage. At the same time, Gingrich's success so far has damaged Mitt Romney's campaign, badly hurting an establishment candidate that many of the party faithful already had trouble getting behind. That means either candidate might appear too weak to beat Obama to Republican leaders if they won the nomination or perhaps neither will be actually able to collect a majority of delegates to claim the prize. That is especially likely due to the presence of libertarian Ron Paul in the race further splitting the field and committed to the long haul.

The solution? Someone completely new. "You're just not going to have a winner in this primary process. I'm looking for a brokered convention," former Republican congressman Dick Armey told CNBC recently, referring to a process whereby convention delegates in Tampa could choose a nominee via a process of bargaining and deal-making. At the same time Bill Kristol, the highly influential editor of the conservative bible The Weekly Standard, has been openly advocating for Daniels to get into the race, even writing a column headlined: "Debate winner: Mitch Daniels" after the latest televised debate in Florida.

The conservative Washington Post columnist Jennifer Rubin has penned an open letter to 10 top Republicans, begging them to do everything they can to stop Gingrich. "One of you can run yourself. Or you can collectively get behind a not-Gingrich candidate," she wrote.

Most experts still see such events as unlikely. "One of these candidates is still likely to go to Tampa with a majority of delegates, and the favourite is still Romney," says professor Gregory Magarian, an expert on the US political system at Washington University. Still, there are several possible, though unlikely, ways for an outsider to enter and maybe win:

A new hope

The most difficult would be a late entry by a fresh candidate who sweeps into the race and wins the remaining contests to collect enough delegates to take to the Tampa convention and earn the nomination. However, that is almost impossible due to the passing of many deadlines for entry in some states still to come. Even Gingrich himself failed to get on the ballot in a huge state like Virginia.

The white knight

A more plausible plan would be for an outsider to join late in the race, fight in whatever states he or she can, and then go to Tampa with enough delegates to prevent any other candidate from winning outright. In the following bout of horse-trading and backroom deals, that candidate could pose as the "unity" choice to bring together a party fractured between competing Romney, Gingrich and Paul camps. "There would come a point in the race where it would be a free for all and at that point someone like Mitch Daniels comes in as a white knight," says Magarian.

The undeclared

Another possibility would be for an outsider candidate to stay outside the race until Tampa and then declare themselves at the convention as all other candidates fail to secure a majority of delegates and fail to get behind a rival. The disadvantage of that would be the selection of a nominee for whom no Republican primary voters or caucus goers actually voted. That would dishearten Republicans and likely prove an electoral gift for the Democrats. "A lot of voters would be very sceptical of someone who has not been vetted by the nomination process," says Magarian.

Brokered conventions used to be common in US politics. But the last truly brokered convention in American politics happened in 1952. Since then there have been many predictions of such a possibility. But one has not fully come to pass in half a century despite some close calls. The race between Obama and Hillary Clinton in 2008 was often predicted to turn into a brokered convention, especially due to the role of "super delegates" who are party officials and other leaders who have a vote in the convention alongside all the elected delegates from the individual states. However, in the end, the Democratic party establishment super delegates abandoned Clinton and got behind Obama who also managed to win a majority of elected delegates anyway.

But Tampa could be different. Republican super delegates are likely to be hostile to Gingrich's insurgent campaign. Yet if they sided with the Romney campaign in order to get the nomination away from the former speaker it would likely provoke an outcry from Gingrich's supporters.

Some experts believe that means another scenario becomes possible if the Republican vote remains hopelessly divided amid an increasingly bitter fight. "What's more likely is someone going for a third party run," says professor Cary Covington, a political scientist at the University of Iowa. Ron Paul is the usual suspect there, despite his repeated denials of such ambitions.

But, if Gingrich wins the Republican nomination outright, it is not hard to imagine a more moderate Republican leaping in to go it alone. Or, if Romney wins or Gingrich is denied the nomination by back room dealing, perhaps the speaker would launch his own bid, backed by wealthy supporters. That would almost certainly be a Republican nightmare and a Democrat dream.