Ben Carson has seized the national lead from Donald Trump in a new poll, in a development sure to force the billionaire businessman to modify his well-polished campaign stump boast that he's "leading every poll." 

Released ahead of Wednesday's third Republican presidential primary debate, the CBS News/New York Times Poll showed Carson leading nationally with 26 percent, to Trump's 22 percent. 

The survey follows a string of Iowa polls that showed the retired neurosurgeon pulling ahead in the first-in-the-nation caucus state. Trump, who had led the field nationally and in key states since the summer, has tried to downplay the results but on Tuesday acknowledged Carson is gaining momentum. 

"Ben Carson is now doing well," Trump said in an interview Tuesday morning on MSNBC. 

At the same time, Trump has made clear he plans to challenge Carson at Wednesday's primary debate as the two battle for the top spot. 

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Trump previously called Carson "low energy" and questioned his immigration stance. On Tuesday, he predicted Carson would have to deal with more scrutiny from all directions. 

"One thing I know about a frontrunner, you get analyzed 15 different ways from China. A lot of things will come out," he said. 

He continued to tout his own numbers and support. 

"I have tremendous crowds and tremendous love in the room and, you know, we seem to have hit a chord. But some of these polls coming out, I don't quite get it. I was No. 1 pretty much in Iowa from the beginning, and I would say we're doing very well there. So I'm a little bit surprised," he said. "The other polls, as you know, in other states are extraordinary." 

The most recent Iowa poll showing Carson ahead was conducted by Monmouth University and released Monday. It showed Carson leading Trump by 14 points, his biggest lead to date. 

Trump has led the Republican field nationally in almost every poll until now. 

The CBS News/New York Times survey showed the rest of the candidates trailing in single digits. Florida Sen. Marco Rubio was in third with 8 percent, followed by former Florida Gov. Jeb Bush and former HP chief Carly Fiorina with 7 percent. 

The poll of 575 GOP primary voters was taken Oct. 21-25, and had a margin of error of 6 percentage points.