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Carly Fiorina′s swell of support after her strong debate performance last month has collapsed, according to a new CNN/ORC poll that showed rivals Donald J. Trump and Ben Carson benefiting from her waning popularity.

The survey found Mr. Trump and Mr. Carson leading the crowded field with the support of 27 percent and 22 percent of registered Republicans. The poll, released on Tuesday, had a margin of error of five percentage points.

The numbers were bad news for Mrs. Fiorina, the former chief executive of Hewlett-Packard, who stood up to Mr. Trump during the last Republican debate and won accolades for her crisp, forceful performance. However, her bounce in the polls appears to have been ephemeral, and her support has dropped to just 4 percent, from 15 percent in September, the poll showed.

Mr. Trump’s support seems to have stabilized after showing signs of leveling off in recent weeks, and Mr. Carson continues to see his prospects improve after provocative remarks he made about Muslims and gun control.

Otherwise, the CNN poll showed the dynamics of the Republican field largely unchanged. Jeb Bush and Senator Marco Rubio were tied for third place at 8 percent, while the other candidates remained locked in the low single-digits.

CNN’s results were similar to a poll released on Monday by NBC and The Wall Street Journal that found Mr. Trump and Mr. Carson atop the field, with a quarter of Republican voters backing the billionaire developer.