Poll: Donald Trump and Ben Carson now neck-and-neck

Another sign that Donald Trump is fading -- and Ben Carson is rising.

The billionaire businessman and the retired neurosurgeon are in a virtual tie, according to an NBC News/Wall Street Journal poll released Sunday.

Trump is at 21% and Carson is at 20%, a difference well within the poll's margin of error; Trump has been leading a variety of Republican polls for more than two months.

Meanwhile, another "outsider" candidate -- businesswoman Carly Fiorina -- is tied for third place with Sen. Marco Rubio, R-Fla., both at 11%.

In fifth place: Former Florida governor Jeb Bush (7%), followed by Ohio Gov. John Kasich (6%), and Texas Sen. Ted Cruz (5%).

No other Republican received more than 3% support in the NBC News/Wall Street Journal poll.

From NBC News:

"Back in July's NBC/WSJ poll, Trump was in first place at 19 percent, Scott Walker (who exited the race on Monday) was second at 15 percent, Bush third at 14 percent and Carson fourth at 10 percent. Rubio was just at 5 percent, and Fiorina didn't register at all in the poll.

"Adding both first and second choices, Carson tops the current GOP field at 35 percent - followed by Trump at 31 percent, Fiorina at 28 percent, Rubio at 26 percent and Bush at 19 percent."