The national survey, conducted ahead of Thursday’s first presidential debate, shows almost two-thirds of registered voters who identify as Republican and back the billionaire would definitely or probably support him in a third-party bid.

Trump is the first choice of 21 percent of that group, more than twice the national support of his nearest rival, former Florida Governor Jeb Bush, the poll found. Trump’s strength has been fueled by both his celebrity status and his ability to tap into an unhappy and unsettled electorate amid a historically crowded field of candidates.

None of this means an independent bid looks promising for Trump, at least at the moment. Nineteen percent of respondents said they would definitely or probably vote for him if he ran as a third-party candidate in a general election. The real estate magnate, now leading in national Republican polls, hasn’t ruled that possibility out.