By Tal Kopan, CNN
Washington (CNN)Donald Trump is expanding his strong lead over the other GOP presidential candidates nationally, according to a new poll, but Ben Carson is also posting a big jump in support.
In the first national Monmouth University pollout since the first Republican presidential debate, released Thursday, the real estate mogul is showing a commanding lead at 30% support. That’s up 4 points from a poll taken just before the debate last month, but within the poll’s margin of error.
It’s also a new high for Trump, narrowly topping the 28% support he registered in a Quinnipiac poll late last month.
But Carson, a neurosurgeon, posted the biggest gain in support since August, jumping 13 points to second place. He is holding down 18% support now among Republicans. That continues a trend of recent polls that show him moving up the list.
It’s also Carson’s highest recorded number in a national poll, topping a 13% mark in a Fox news poll this spring.
Trump’s lead also evaporates when the field is narrowed to just him and Carson. Asked about a head-to-head match-up between those two, Republican voters picked Carson over Trump, 55% to 36%.
Carson was the only candidate to beat Trump in a head-to-head, the poll found.
The poll confirms recent trends of Trump’s lasting lead and Carson’s surge — as well as steep drops in support for some more establishment candidates.
Former Florida Gov. Jeb Bush fell out of second place, dropping from 12% support in August to 8% now, though that fall is within the margin of error. That tied him for third place with Texas Sen. Ted Cruz.
Wisconsin Gov. Scott Walker also fell. He was in third place at 11% in August, and dropped 8 points to just 3% on Thursday.
Florida Sen. Marco Rubio was in fourth place at 5% and businesswoman Carly Fiorina and former Arkansas Gov. Mike Huckabee tied in the fifth spot at 4%.
The poll also found corresponding shifts in candidates’ favorability scores.
Both Trump and Carson saw their favorability ratings grow. Fully two-thirds of voters rated Carson favorably, up 22 points from August, and only 6% viewed him unfavorably. Trump was viewed favorably by 59% of Republican voters, up 7 points from August, and unfavorably by 29%.
Bush’s favorability, on the other hand, ebbed by 11 points since August. He was at 41% favorably to 39% unfavorably, essentially even given the poll’s margin of error.
Monmouth surveyed 366 Republican voters between Aug. 31 and Sept. 2 by telephone interview for the poll, which has a margin of error of plus or minus 5.1 percentage points.