My colleague (and boss) Nate Silver believes Jeb Bush is “probably toast.” He isn’t alone: A bunch of pundits are saying Bush is finished. I’m not sure I would go that far; there is no clear front-runner in either the endorsement race (which Bush nominally leads) or the money race (which Bush also leads, if you count super PAC money). With the Republican field in such disarray, I’m hesitant to predict anything with certainty.

But while I don’t think Bush’s demise is a fait accompli, I definitely agree that he’s in serious trouble. Bush isn’t going to win any primaries if his popularity among Republicans continues to plummet.

No candidate’s net favorability — the share of Republicans who view a candidate favorably minus the share who view him or her negatively — has fallen more than Bush’s since mid-June, when Bush and Donald Trump entered the race. Here are all the candidates’ net favorability ratings over that span, in a chart we put together before Wednesday’s Republican debate.

Bush’s net favorability has dropped 28 percentage points since mid-June, while the average candidate’s net favorability declined by just 5 percentage points.

Bush’s falling favorability is, of course, a very bad sign for his candidacy. It suggests that Bush’s fall in the horse-race polls isn’t merely due to other candidates doing better. Instead, Bush seems to be doing worse. Put another way, the more Republican voters get to know Bush, the less they seem to like him. Attacking other candidates, such as when Bush went after Marco Rubio on Wednesday night, is unlikely to solve Bush’s problem.

Right now, Bush’s net favorability, per YouGov, is better than just two other candidates who appeared in the main-stage debate: Chris Christie and Rand Paul. It’s worse than Trump’s, whose net favorability is far below what we’d expect of a future nominee based on his high name recognition.

But here’s one ray of hope for Bush: Trump has already proven that voters can change their mind about a candidate quickly. Trump’s net favorability has spiked and plummeted multiple times. Of course, Republicans have been changing their mind about Bush — just all in a negative direction.