Washington, March 3 As the reality of the Donald Trump train rumbling towards Republican presidential nomination after his Super Tuesday performance hit the party establishment, it mounted a last ditch effort to stop the unstoppable.

In what analysts described as too little and too late, the party\'s 2012 nominee Mitt Romney was set to take a shot on Thursday at slowing the brash billionaire who has won 10 of the 15 nomination contests so far, including seven of 11 on Tuesday.

Sources cited by CNN said Romney plans \"going after Trump\" to make the point that the frontrunner is the wrong person to lead the Republican Party and underscoring the \"choices facing the Republican Party and the country\" in this election.

Trump responded late Wednesday by mocking Romney in a pair of tweets.

\"Failed Presidential Candidate Mitt Romney is having a news conference tomorrow (Thursday) to criticise me,\" he tweeted. \"Just another desperate move by the man who should have easily beaten Barrack (sic) Obama.\"

But at least one rival, retired neurosurgeon Ben Carson acknowledged that after going 0-for-15 in the first states to vote, he did not see \"a political path forward\" and said he would not participate in Thursday\'s Republican debate hours after Romney speaks in Utah.

Carson, however, stopped short of saying he was officially leaving the race.

Most Republicans in Congress will not embrace Trump as long as there is a possibility, regardless of how slim, that there\'s still another Republican candidate in the race that is trying to take him down, CNN reported.

But the problem for Republicans pushing the anti-Trump effort is that they cannot agree on who the party should elevate as the most effective challenger to Trump, it said.

\"The D.C. establishment is scared to death,\" House member Tom Marino, a Trump supporter told CNN expressing confidence that top Republicans in Washington will eventually come around and work with Trump.

They would not have much choice, he warned as \"the American people are fed up with it and the elected officials, if they don\'t grasp it, they\'ll be out of a job\".

Meanwhile, Trump\'s nearest rival Texas Senator Ted Cruz, who has won four contests so far, also acknowledged that primary loss in his home state would have meant the end of his campaign.

\"Listen, everyone recognises Donald Trump is a unique phenomenon,\" Cruz told reporters in Kansas on Wednesday night.

\"I asked the team what do we do if we lose Texas? And we had reached the conclusion, if we had lost Texas, that would\'ve been the end of the road.\"

Cruz campaign\'s chief strategist, Jason Johnson also asked Trump\'s other rival Marco Rubio to quit should he lose his home state of Florida in the next crucial primary battle on March 15.

Trump leads the Republican delegate count with 315, according to a CNN estimate.

Cruz is in the second lead with 205, and Rubio with 106.

The winner needs to have the support of a majority of the 2,340 delegates in 50 states.

Republican bigwigs trying to stop the Donald Trump train