Trump and Carson are effectively tied when first and second choice preferences are combined. 43% of Republicans choose Trump first or second; 42% say Carson is their first or second choice. Rubio is far behind those two, but runs ahead of Jeb Bush, his Florida colleague. 

The Economist/YouGov Poll includes the responses of 2,000 adults nationwide. The larger sample size means there are about 500 self-identified Republicans, and it is possible to look at subgroups within the party. Trump runs equally well with men and women, though his first choice margin over Carson is bigger among men than it is with women. Carson runs ahead of Trump in the Midwest; Trump leads in all other regions. 

41% of Republicans this week believe Trump is their party’s likely nominee. And three in four Republicans think he can defeat the Democratic nominee, whomever that is. But Trump is not the only Republicans thought of as a possible fall winner. As many think Carson could win as think Trump can; Majorities of Republicans also see Rubio and former Florida Governor Jeb Bush as possible winners.