As the Republican Party establishment coalesces around Marco Rubio as its choice for the presidential nomination, voters have continued to stick with Donald Trump.

And there's reason to believe that won't change.

The campaign moves on to Nevada on Tuesday for the state's Republican caucuses, following the party's primary in South Carolina on Saturday. That vote was won handily by the businessman Trump with just under a third of ballots cast in his favour, while Rubio, a senator from Florida, narrowly finished second ahead of Texas senator Ted Cruz.

As he had done in the first caucuses of the race in Iowa (but had failed to do in the New Hampshire primary earlier this month), Rubio beat his poll numbers and outpaced his "establishment" rivals comfortably. These results have led party elites to begin to move toward Rubio as the best option to defeat Trump and Cruz, two anti-establishment candidates reviled by the upper echelons of the Republican Party.

This despite the fact that Rubio began his political career as a Tea Party favourite and is considered more conservative than most Republicans.

Nevertheless, Rubio has been piling up endorsements from elected Republicans since the Iowa vote: at least eight sitting senators and three governors, along with over a dozen members of the House of Representatives, adding to an already long list of supporters.

He has also been raising a lot of money, having amassed $85 million, putting him second only to Cruz's $104 million. The big new prize may be the donor base of former Florida governor Jeb Bush, who had raised the most money of any Republican candidate in the campaign before dropping out of the race on Saturday.

But if the party's most influential and wealthiest members are increasingly siding with Rubio, Republican voters aren't.

Not yet, at least.

The latest national polls, conducted before the South Carolina primary, give Trump about 35 per cent support among Republican voters, followed by Cruz at 19 per cent and Rubio at 15 per cent. Neurosurgeon Ben Carson and Ohio Gov. John Kasich round out the list with eight and seven per cent support respectively, according to FiveThirtyEight's weighted averages.

Polls out of Nevada suggest Trump could win by as many as 20 points. He is also favoured in almost all of the states voting on "Super Tuesday," March 1, when a large swath of the country will cast ballots in both the Democratic and Republican races.

Trump's ceiling may not be so low

Though Trump's polling at the national level has struggled to increase much beyond the support of one in three Republicans, he still has some potential for growth. His favourability ratings are low, even among Republicans, but he does garner enough second choice support in polls to keep his theoretical ceiling above those of his rivals.

Trump is not the consensus second choice of Republicans. In recent polls he has ranked behind Cruz and Rubio on that score. But he is still the second choice of around a tenth of those polled. While that is half of what Cruz and Rubio manage, it is enough to put his ceiling somewhere around 45 to 50 per cent among Republicans if his first and second choice numbers are combined.

That is more than enough to win the nomination, particularly considering that both Cruz and Rubio appear to have a ceiling that is no higher than 40 per cent. In addition, some states have winner-take-all primaries, as South Carolina did — despite taking 32.5 per cent of the vote, Trump won 100 per cent of the state's delegates.

Winnowed field helps Rubio, but Trump too

The Republican establishment hopes that Rubio's chances will improve as the field of candidates dwindles. Chris Christie, another establishment favourite, dropped out after New Hampshire. Bush's departure after the South Carolina vote also frees up some Republicans, though the five per cent support he had in national polls is hardly game-breaking.

GOP 2016 Debate

Trump speaks to Rubio during the CBS News Republican presidential debate at the Peace Center, on Feb. 13 in Greenville, S.C. (John Bazemore/Associated Press)

It is likely that Rubio will capture many of Bush's supporters. Second choice polling suggests that about one-fifth of Bush's supporters will go his way, while Kasich could take a similar chunk of support. 

But the problem for Rubio is that he trails Trump by such a wide margin that there isn't enough support among establishment candidates to tilt the balance in his favour. Even if all Republicans who supported Bush and those who currently support Kasich (the most moderate candidate still in the race) went over to Rubio, he would still trail Trump by a fair margin.

And all of that support won't go to Rubio. The polls suggest that a tenth could go to Trump and perhaps a little more to Cruz. These two candidates would also likely take most of Carson's support if he drops out of the race as well.

Some polling done listing just the three leading Republican candidates still puts Rubio at a big disadvantage against Trump.

This means that a winnowed field alone will not win the nomination for Rubio. Trump still has enough support among Republican voters to hold off a single establishment candidate, particularly if Cruz stays in the race for the long haul. And Trump is poised to pile up a lot of delegates next week before a candidate like Kasich might drop out (his state of Ohio votes on March 15).

Instead, for Rubio to prevail he will need to start taking votes not only from the establishment-friendly candidates that have withdrawn or might drop out of the campaign, but also from Cruz and Trump. That means going after those two candidates and their supporters.

The anti-establishment tide in the Republican presidential contest is strong enough to sweep aside all before it. Rubio now has to row against that current — with the backing of the very establishment his opponents are railing against.