Mr. Carson, a retired neurosurgeon, is the choice of 26 percent of Republican primary voters, the poll found, while Mr. Trump now wins support from 22 percent, although the difference lies within the margin of sampling error.

The survey is the first time that Mr. Trump has not led all candidates since The Times and CBS News began measuring presidential preferences at the end of July.

No other candidate comes close to Mr. Carson and Mr. Trump. Senator Marco Rubio of Florida received 8 percent while former Gov. Jeb Bush of Florida and Carly Fiorina, the former Hewlett-Packard chief executive, are each the choice of 7 percent of Republican primary voters.