The new NBC News/Wall Street Journal poll shows the billionaire real estate mogul still leading all GOP rivals with 25 percent of the vote. In September, he drew 21 percent. That change falls within 4.9 percent margin for error in the survey of 400 Republican primary voters.

When considering the various candidates' potential for expanding their support, the poll tells a different story. When Republican voters are asked to name their second choice in the race, 22 percent name Carson, compared with 14 percent for Trump, 13 percent for Rubio and 10 percent for Fiorina.



Thus if candidates are ranked by the combination of voters naming them either first or second, Carson draws 44 percent to Trump's 39 percent, Rubio's 26 percent and Fiorina's 18 percent.

Using another measure, 74 percent of all Republican voters allow for the possibility that they could support Carson. Some 65 percent say the same of Rubio, 59 percent of Trump, 56 percent of Fiorina and 51 percent for Bush.