Donald Trump sits firmly atop the Republican primary field one week before the inaugural GOP debate, according to the Quinnipiac Poll released Thursday.

The bombastic reality television star and real estate magnate has the support of 20% of Republicans, according to the poll, with Wisconsin Gov. Scott Walker following at 13% and former Florida Gov. Jeb Bush rounding out the top-3 at 10%. No other Republican candidate polls higher than 6%, with nine of the 12 remaining candidates polling within a statistical tie according to the survey.

The poll is likely to be one of the five surveys that will factor in determining eligibility for the GOP debate, with the Fox News using an as-yet-unknown method for averaging the results. The network has said it may allow more than 10 candidates on stage in the event of a tie.

The close results highlight the challenges inherent to using polling to attempt to winnow the massive Republican primary field.

Retired neurosurgeon Ben Carson, former Arkansas Gov. Mike Huckabee, Sen. Rand Paul, and Sen. Marco Rubio each polled at 6%, followed by Sen. Ted Cruz and Ohio Gov. John Kasich at 5%. New Jersey Gov. Chris Christie polled at 3%, rounding out the top 10, with Louisiana Gov. Bobby Jindal and former Texas Gov. Rick Perry earning 2% each. Former Sen. Rick Santorum, former HP CEO Carly Fiorina, and former New York Gov. George Pataki each pulled in 1%.

Among Republicans, 30% said they would under no circumstances vote for Trump—the highest of any candidate—with 15% saying they would never back Christie and 14% saying the same of Bush. Trump is viewed favorably by 50% of GOPers, with 33% viewing him unfavorably—among the lower net figures in the GOP field. Christie, though, is even worse, with 40% holding positive views and 37% negative.

Rubio and Walker remain the most beloved in the GOP, with more than three-fifths holding favorable opinions of the candidates and just single digits viewing them unfavorably. Bush saw a significant jump to his approval ratings, from the last Quinnipiac survey in May, rising from just 28% viewing him favorably to 43%, with the percentage viewing him unfavorably declining from 44% to 41% over the same period.

Americans of all stripes believe Trump possesses strong leadership qualities, with 58% of Americans and 61% of independent voters agreeing with that statement. Yet on two other key metrics of candidate performance, trust and caring about voters, Trump is underwater by roughly 2-1 margins.

The poll of 710 Republicans was conducted from July 23-28 and has a margin of error of ± 3.7 percentage points. The broader sample of 1,644 registered voters has a margin of error of ± 2.4 percentage points.

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