Story highlights

Donald Trump captured 21% compared to Ben Carson's 20%

Hillary Clinton -- who held a 60-point lead over Bernie Sanders in June -- has slipped to a 7-point advantage over the Vermont senator

Washington CNN  — 

Businessman Donald Trump and retired neurosurgeon Ben Carson are running neck-and-neck in the race for the GOP presidential nomination, while former Secretary of State Hillary Clinton continues to lose ground to Vermont Sen. Bernie Sanders, a new NBC News/Wall Street Journal national poll has found.

Trump remains on top in the GOP field, capturing 21% of Republican primary voters, but Carson is at 20%, within the poll’s margin of error.

RELATED: In blue New Hampshire, doubts about Clinton grow in new poll

Former tech CEO Carly Fiorina and Florida Sen. Marco Rubio tie for third at 11% each, with former Florida Gov. Jeb Bush (7%), Ohio Gov. John Kasich (6%) and Texas Sen. Ted Cruz at (5%) rounding out the rest of the field. No other Republican received more than 3%.

On the Democratic side, Clinton – who held a 60-point lead over Sanders in June – has slipped to a 7-point advantage over the Vermont senator among Democratic primary voters, 42% to 35%. Vice President Joe Biden, who has not yet declared whether he will seek the Oval Office, comes in third with 17%. No other Democrat received more than 1%.

When Biden is removed from the equation, Clinton’s lead swells to 53% to Sanders’ 38%.

RELATED: Poll finds a new top tier for New Hampshire GOP primary

The NBC/WSJ poll was conducted Sept. 20-24, mostly after Scott Walker dropped his candidacy. Those surveyed included 256 Democratic voters (which had a margin of error of plus-minus 6.1 percentage points) and 230 GOP primary voters (plus-minus 6.5 percentage points).