THE presidential campaigns are moving into a cluster of delegate-rich state primary elections and caucuses, with Republican billionaire businessman, Donald Trump and Democrat Hillary Clinton, the former secretary of state, gathering momentum.

Mr. Trump, the brash New Yorker, had a resounding victory in South Carolina on Saturday, sweeping all 50 delegates. Heading into Tuesday’s Republican caucuses in Nevada, he has 67 delegates. Since his key opponents, Texas Senator Ted Cruz and Florida Senator Marco Rubio, took no delegates in South Carolina, they are left with a total of 11 and 10, respectively. It takes 1,237 to capture the nomination.

Mr. Rubio is battling to set himself up as the candidate of the party establishment now that former Florida Governor Jeb Bush is out of the race. The more conservative Mr. Cruz, who is not liked by the party’s establishment, is unlikely to finish above second or third in the coming contests, except in his home state of Texas.

With roughly 70 per cent of Republicans in national polls declining to back Mr. Trump, Mr. Cruz and Mr. Rubio are trying to cast themselves as the one candidate around whom what Mr. Rubio calls the “alternative-to-Donald-Trump vote” can coalesce.

A close look at the election calendar suggests that if Mr. Trump’s rivals don’t slow him by mid-March, their only chance to deny him the Republican presidential nomination may be a nasty and public fight at the party’s convention this summer.