Not only did Trump secure another thumping victory, but the establishment's most significant hope for a unifying figure, Marco Rubio, practically tied for second place with another insurgent, Ted Cruz.

Indeed the only good news for the party's ruling class was the end of the race of its humbled favoured son, Jeb Bush.

Pressure will now mount on other candidates, like John Kasich and Ben Carson, to leave the race to clear the way for Rubio. But both confirmed on Saturday night that they would do no such thing.

And even if they did, it is not clear that Rubio can beat Trump.

From the outset of his campaign, the freshman senator who was born of the Tea Party only to be embraced by the establishment talked of his 3-2-1 strategy: He would come third in Iowa, second in New Hampshire and first in South Carolina, at which point he would come to be seen as the presumptive nominee.

As it played out, the young Cuban-American came third in Iowa, fifth in New Hampshire and with most of the vote counted, second in South Carolina.

Before Saturday night's poll he managed to win massive support from the South Carolina Republican machine, securing the crucial endorsement of the state's popular governor, Nikki Haley.

Senator Tim Scott, the only African-American Republican in the Senate, and congressman Trey Gowdy, who has led the party's fight to link Hillary Clinton to the deaths of four American diplomats in Libya in 2012, both campaigned for Rubio alongside Haley. To many in South Carolina, it looked like an all-star team of Republicans who could deliver the state for Rubio.

Rubio's machine and independent groups supporting it spent $12 million campaigning in South Carolina. By contrast, Trump spent the week slaughtering sacred cows and indulging in his penchant for trenchant bigotry.

During a Republican debate he engaged in the heresy of blaming the September 11 attacks on George W. Bush, then he took on the Pope, who had dared suggest his immigration policy was un-Christian. Then he regaled his supporters with a false story about "Black Jack" Pershing's execution of Muslim prisoners in the Philippines using bullets dipped in pig blood.

He spent just $1.78 million. And then he stormed home to a victory of at least 10 percentage points.

This can't have escaped the party's establishment. Nor can the lessons of history.

No Republican has ever won emphatic victories in New Hampshire and South Carolina and not gone on to win the party's nomination. It is now impossible to see Trump as anything but the favourite.

And then there is the sheer scope of the rebellion in the party. Both Trump and Cruz ran hard against the Republican establishment, which Cruz likes to call "the Washington cartel". Combined, their vote was around 55 per cent.

For the Democratic Party's centrists the news on Saturday was better. Hillary Clinton held on to her significantly diminished lead to win the caucuses in Nevada by 5.3 per cent over Bernie Sanders.

This was not the victory that was expected a month ago, but after Sanders' drubbing of Clinton in New Hampshire, it was significant.

Clinton remains the overwhelming favourite to win the Democratic primary in South Carolina next Saturday, and after that to dominate Sanders in a string of states on March 1.

Sanders' support is considerable and passionate, and his campaign will go on. But it is now even harder to see his path to victory.