History shows the Republican candidate who wins most of the states on Super Tuesday wins the nomination.
And so Donald Trump is now on course to stand on the stage in Cleveland, Ohio, in the summer and follow in the footsteps of Nixon, Reagan, Bush (both of them), Dole and McCain.
His rise has been spectacular and surprising.
He wondered about running for president in 2000 for the Reform Party. But eventually he decided not to seek the nomination saying it was too splintered to mount a successful run at the White House.
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He also didn't like the main figures in the party. One was Pat Buchanan, a former Nixon speechwriter who twice attempted to secure the Republican presidential nomination himself - he was accused of anti-Semitism while disputing the numbers of Jews killed by the Nazis at the Treblinka death camp.
Another was David Duke; at one point a prominent Republican politician in Louisiana, but perhaps better known as the former Grand Wizard of the racist Ku Klux Klan. Trump left saying, "That is not the company I wish to keep".
Yet, when asked about David Duke expressing support for Trump's election campaign this week, the billionaire businessman said that he had no idea who Duke was. He didn't initially disavow his support. And he claimed that he didn't have enough information about white supremacist groups to reject any endorsement they might offer.
Within hours - and perhaps aware of the storm that he had created, Trump eventually rejected Duke's backing.
The Southern Poverty Law Center ,which tracks hate groups in the US, were astounded by Trump's claims. Mark Potok, a senior fellow with the group, speaking from its headquarters in Alabama, said the idea Trump had to look up the Klan was "astounding".
He added: "I've never seen anything like that in mean stream politics, literally, for decades."
Trump has managed to harness a visceral anger in the US, where people feel politicians have failed to deliver on promises, where they are ignored and the system and the economy is rigged against them.
A similar anger has helped propel the Bernie Sanders campaign on the Democrats side.
Potok tried to explain it like this: "There is a large working-class and lower-middle-class white America who feel they are in trouble and they feel they country is changing around them and they're angry".
And he believes Trump was initially reluctant to repudiate the Klan on the chance that would impact on the constituency he was trying to reach.
Controversy after controversy
Throughout this campaign, Trump has attacked and attacked.
He launched his campaign claiming many of the immigrants making their way from Mexico were "murderer and rapists"; he mocked a disabled reporter; he called Iowa voters stupid and dismissed former Republican presidential hopeful, John McCain, a man who was a prisoner of war during Vietnam, as a "loser" because he was captured by the North Vietnamese; he got involved in a spat with the Pope over his plans to build a border wall with Mexico; and he famously announced that he wanted to stop all Muslims temporarily entering the US.
Each and every time he has made the comments, the crowds have roared with approval.
And despite people thinking that each new controversy would finish his campaign, he's gotten stronger and bolder.
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For many of Trump's supporters, the past eight years have brought massive changes: there is a black man in the White House; gay marriage has been legalised; and a form or universal healthcare has been introduced.
One columnist in Houston, Cory Garcia, argues that Trump is the best thing to happen to American politics, believing the businessman has exposed a dark underbelly.
Sitting in a conference room at his weekly paper, The Houston Press, he told me: "Donald Trump is the answer to, I think, a lot of Republican questions about 'what would happen if we were just honest? What if we didn't beat around the bush about race, or immigration, or terrorism? What if we just said what we meant? Like, would we be punished for that? Would people be, would we be isolated, would we be marginalised? And the answer is, at least to Republican voters, no.'"
For Trump, there is no coded language, no hidden message, no dog whistles that only Republicans understand.
It's all there, on show and the people respect his blunt, unvarnished presentation. He doesn't care who he upsets.
And the people have responded with support and more importantly, votes.
The Republican establishment thought Trump's campaign would fall apart. He didn't have the discipline. He didn't have the organisation.
Now, they are deeply worried he will be the party's standard bearer in November's presidential election.
And after Super Tuesday, that is more likely than not.
Source: Al Jazeera