Former Florida Gov. Jeb Bush apparently is out of the top tier of Republican presidential contenders, a Wall Street Journal/NBC poll indicated Sunday. Retired neurosurgeon Ben Carson and former Hewlett-Packard CEO Carly Fiorina surged into the vaccuum while real estate mogul and celebrity candidate Donald Trump retained his front-runner status, the poll of 1,000 people Sept. 20-24 indicated.

Bush has gone from a frontrunner to a sideshow. "Some 7 percent of Republican primary voters named Mr. Bush as their top pick for the GOP nomination, down from 14 percent in July and 22 percent in June," the Journal reported.

Fiorina, riding the wave of attention and praise following a strong performance on CNN's second Republican presidential debate Sept. 16, scored 11 percent as did Florida Sen. Marco Rubio.

Carson is almost matched with Trump, taking 20 percent of GOP primary voters' support compared to Trump's 21 percent. It's a major jump for Carson after the last Journal/NBC News poll in July in which Carson only polled at 10 percent. The Journal noted when voters’ first choices are combined with their second, Carson actually overtakes Trump.

Significantly, the poll was conducted after Carson's inflammatory remark that a practicing Muslim should not be allowed to become president. After much criticism, Carson doubled down on that statement Sunday on CNN's "State of the Union."

"I would have problems with somebody who embraced all the doctrines associated with Islam," he said, "if they are not willing to reject Sharia and all the portions of it that are talked about in the Quran."

On the Democratic side, meanwhile, 17 percent of primary voters say Vice President Joe Biden would be their pick if he ran. Hillary Clinton dropped from 53 percent to 42 percent when Biden -- who has not yet said whether he will run -- was listed as a potential challenger. Vermont Sen. Bernie Sanders stayed at 35 percent when Biden was included in the lineup, "compared with 38 percent when [Biden's] not in the mix."

The survey included 230 likely Republican primary voters and 256 likely Democratic primary voters. The margin of error on the GOP side was 6.46 percent, while on the Democratic side it was 6.13 percent.