Ben Carson is on fire - and he's almost pulled even with Donald Trump

Retired neurosurgeon Ben Carson has pulled to within 4 points of Republican presidential front-runner Donald Trump in a new survey of the Republican presidential race, continuing a dramatic surge over the past month.

A new CBS/New York Times poll released Tuesday found Carson rising to 23% support among national Republican primary voters, a 17-point increase over the past month. He's nipping at the heels of Trump, who grabbed 27% of the support of Republican primary voters.

Together, the two political outsiders combine for half the GOP primary vote at this point in the race. Far behind them in third place are former Florida Gov. Jeb Bush (R), former Arkansas Gov. Mike Huckabee (R), and US Sen. Marco Rubio (R-Florida), who each earned 6%.

Wisconsin Gov. Scott Walker (R), once an early favorite to win the Republican nomination, saw the most dramatic fall over the past month. He has plunged from 10% support in August to just 2% now. Bush has also lost about 7 points of his backers since August. Carson's rise suggests he garnered at least some support from previous backers of Bush and Walker.

"GOP primary voters have yet to show much appetite for or excitement about their establishment candidates, instead rallying behind 'damn the system' candidates," Ben LaBolt, a veteran Democratic strategist who worked on both of President Barack Obama's campaigns, told Business Insider recently. "The rise of Carson and Trump suggests Bush, Rubio, et al. face a much steeper path than anticipated."

Trump still leads with most demographics within the Republican Party. But in some areas there, too, Carson is catching up. For example, he now leads Trump among Republican college graduates by an 8-point margin. However, Trump, according to the poll, still holds significant leads over Carson among men, evangelical voters, and voters who have not graduated from college.

The poll's release comes a day before the second Republican presidential debate in California, where Trump will again take center stage. And Carson will be in a bigger spotlight after he dazzled during the first debate.

Since that performance, Carson has steadily risen nationally and in polls of key early-voting states like New Hampshire and Iowa. A Monmouth University poll of New Hampshire GOP primary voters released Monday, for example, found Carson trailing Trump 28-17 in the Granite State. And a separate Monmouth poll of Iowa last week revealed that Carson and Trump were in a virtual statistical tie there.

In another national poll recently, Carson was by far the strongest contender to Trump, who dominated almost every other of his Republican rivals. The poll showed Carson was the only candidate with a stronger image than Trump among Republican voters nationally.

The survey also found that Carson is the only candidate to whom Trump would lose a theoretical head-to-head matchup. In fact, Republican voters would prefer Carson to Trump by a 19-point margin if they were the final two candidates in the primary.