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Despite a debate performance last week that some analysts described as lackluster, Donald J. Trump is holding on to his lead in the field of Republican presidential candidates, according to two polls released on Thursday.

A survey of registered Republicans by Bloomberg Politics found that Mr. Trump’s support held steady at 21 percent, unchanged from a month ago, while Ben Carson (16 percent) and Carly Fiorina (11 percent) saw big increases. Jeb Bush, the former Florida governor, also saw an uptick, coming in third place with 13 percent.

The poll represents another indication that Republican voters are craving a political outsider to bring reforms to Washington.

“At some level, it is a risk to elect a person with no experience in government,” said J. Ann Selzer, who conducted the survey. “Republicans, especially, seem ready to take that risk.”

On the Democratic side, the dynamics remain less volatile, with Hillary Rodham Clinton garnering support of 33 percent of Democrats, trailed by Senator Bernie Sanders of Vermont with 24 percent and Vice President Joseph R. Biden Jr. with 25 percent. The polls have a margin of error of 5 percentage points.

A separate poll from Quinnipiac University shows Mrs. Clinton holding a more commanding lead among Democrats. In that national survey she has support of 43 percent of registered or Democratic voters, with Mr. Sanders at 25 percent and Mr. Biden at 18 percent. If Mr. Biden does not run, more of his support will shift to Mrs. Clinton, according to the poll.

Quinnipiac also finds Mr. Trump retaining his lead, with support of 25 percent of Republicans. Mr. Carson and Mrs. Fiorina follow with 17 percent and 12 percent. The survey found that most thought that Mrs. Fiorina won last week’s debate and that Mr. Trump gave the worst performance.

In head-to-head matchups, Mrs. Clinton trails Mrs. Fiorina, Mr. Carson and Mr. Bush, while narrowly beating Mr. Trump. Voters continue to have serious questions about the honesty of Mrs. Clinton and Mr. Trump.

The Quinnipiac poll, which has a margin of error of four percentage points for Republicans and Democrats and three percentage points over all.

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