Party members are now wondering if anything stands in the way of the man many in the party want to disown from becoming their presidential nominee in July.
Another day, another victory speech for Donald Trump, this time after cruising to a win at the Nevada caucus with almost half of the vote.
The billionaire businessman has singled out and thanked voters from across his support base.
"We won the evangelical. We won with young. We won with old. We won with highly educated. We won with poorly educated -- I love the poorly educated. With the smartest people, with the most loyal people. And you know what I really am happy about, because I've been saying it for a long time: 46 per cent with the Hispanics, 46 per cent. Number one with Hispanics ... I'm really happy about that."
Mr Trump has now won three out of four early nominating contests and has even garnered an endorsement from a Republican member of Congress.
A few months ago, he was considered a rank outsider who would stand little chance against established politicians.
Even promises such as banning Muslims from entering the country and refusing to take part in a January debate have failed to slow the real-estate magnate's momentum.
Coming in second in Nevada was Florida senator Marco Rubio, who attributed his poor showing at the polls to the number of candidates left in the race for July's nomination.
He told the television network NBC most Republicans are not happy about Mr Trump's surprise success.
"First of all, I think you need to take everything that we've applied to the lessons of every other campaign before and throw them out the window. Here's the bottom-line fact: The vast and overwhelming majority of Republicans do not want Donald Trump to be our nominee. And that's evidenced by the fact that your own poll last week showed that, if it came down to me and Donald Trump, I beat him by almost 16 points. So what we have now is a dynamic where, as long as there are four people running, dividing up the non-Trump vote, you're going to get results like what you saw last night."
There has been criticism the intense rivalry between the Cuban-American Senator Rubio and Texas senator Ted Cruz has diverted the pair's attention from Mr Trump.
Ted Cruz has been the only challenger to come close to overtaking the businessman, scraping past him to win the opening Iowa caucus.
Despite finishing a close third behind Marco Rubio in Nevada, he has told his followers he is not ready to give up.
"Now, at this point, we've had four primaries. History teaches us that nobody has ever won the nomination without winning one of the first three primaries. And there are only two people who have won one of the first three primaries -- Donald Trump and us."
The upcoming Texas primary election could be make-or-break for Senator Cruz, who has relied on his supporter base of conservatives and evangelicals.
But a chief investigative reporter with the US political reporting organisation Politico, Ken Vogel, has told the ABC it could already be too late for the party to stop Mr Trump.
"None of his victories, I think, in the grand scheme of things, were expected. He's really shocking the political establishment, defying all political conventions. Whether the establishment is coming to grips with this, the answer is still no. They still want to beat him, and their chances for doing so are diminishing drastically as time goes on and he continues to mount these impressive wins. These other candidates, who've focused on more conventional campaign strategies, had a better chance in some of these states that voted one by one. Now, it gets so big and national that it's tough to do that, and it really incentivises the types of candidates who are able to dominate the media landscape. Trump has really taken that to new levels in a way that we have not seen any presidential candidate before him be able to do so successfully."
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