Sen. Marco Rubio (R-Fla.), left, Ben Carson, Wisconsin Gov. Scott Walker, Donald Trump and Jeb Bush take the stage for the first prime-time presidential debate hosted by FOX News and Facebook at the Quicken Loans Arena on Aug. 6  in Cleveland, Ohio. (Scott Olson/Getty Images)

The big takeaway from this new poll of the Iowa GOP caucuses -- from Monmouth University -- is that Ben Carson has  drawn even with Donald Trump, at 23 percent. And it comes a couple days after another poll showed Carson closing to within five.

That in and of itself is remarkable. Trump's rise was already unbelievable; Carson's is equally so. What's even more amazing, though: The third-place candidate in this new poll is businesswoman Carly Fiorina, who like Trump and Carson has never held public office. In fact, they are the only three hopefuls in the GOP field who can say that, and they are 1-2-3.

In fourth place? Sen. Ted Cruz (R-Tex.), who perhaps more than anybody embodies the outsider mentality from within the U.S. Senate.

The combined vote total of those four candidates? 65 percent.

The combined vote total for Jeb Bush, Marco Rubio, Chris Christie, Scott Walker, John Kasich and Bobby Jindal -- who all come from more establishment-oriented backgrounds and the first four of whom have at times been considered GOP front-runners -- is 22 percent.

And while the split is more pronounced in favor of outsiders in this poll, it's not a new phenomenon. The Des Moines Register/Bloomberg poll over the weekend showed the four outsiders getting 54 percent of the vote, compared to the latter sextet's 26 percent. That's still more than two-to-one.

The Monmouth poll also asked people whether they preferred a candidate with experience in government or whether they want "someone outside of government who can bring a new approach to Washington."

Fully 66 percent chose the latter. And they are putting their poll responses where their mouth is.

If you're Bush, Rubio or even Walker, that has to be affecting your calculus in Iowa.