WASHINGTON—Two hours before the Republican presidential debate on Wednesday, a party strategist, Rick Wilson, posted a cryptic message on Twitter.

“Man oh man,” Wilson wrote. “The dumb, preplanned move a certain campaign is about to make in the big debate is campaign-ending stupid.”

Predictably, the candidate about to make the dumb, preplanned move was Jeb Bush. Within seconds of him actually doing it, pundits were declaring the end of his campaign.

“Jeb’s Dead: Adiós Amigo,” read a headline on the website of the conservative Weekly Standard.

Ten months ago, the former Florida governor was the polling front-runner flush with so much Super PAC money he was going to “shock and awe” rivals into submission. He has now become the walking rebuttal to the claim that shadowy billionaires can buy the presidency.

Bush is failing for a host of reasons. Among them: his unpopular last name, his deep ties to the unpopular party establishment, his unpopular desire to let illegal immigrants become legal residents, and his feeble replies to Donald Trump’s merciless emasculation effort.

Above it all, though, there is this: Jeb Bush is just bad at running for president.

“It’s like the difference between a movie star that is handsome and flamboyant, and a really good actor who is — not,” Garry Phillips, the Republican chairman in Tennessee’s Henry County, said in an interview.

George W. Bush, it turns out, is the smooth Bush brother. Jeb, tense and awkward, has managed to turn softball questions on everything from American heroes to superheroes into cringeworthy gaffes.

Perhaps the most predictable question of the campaign was whether he too would have invaded Iraq. When he was asked, in May, he fumbled for an answer for a whole week.

He has gotten less comfortable, not more, over time. His decline in the polls has forced him to play the feisty scrapper, a role that makes him visibly uneasy. He has performed his scripted confrontations with all the enthusiasm of a hostage.

“I think Jeb has a good message. I don’t think he is the orator that he needs to be in order to get that message to the people,” said Buddy Burkhardt, the Republican chairman in Knox County, Tenn. “I think he’s saying the right words, but …”

Before the debate on CNBC, Bush decided he would resurrect his campaign by going after the Senate attendance record of Marco Rubio, the senator who was once his protégé.

Rubio, like Wilson, knew it was coming. He dismissed Bush with a kind of pitying contempt, saying Bush was only making the argument because someone had told him it might help him in the polls.

Bush barely spoke the rest of the night. He seemed, again, like every bit the “low-energy” man Trump says he is.

“Rubio had a great retort, and Jeb just kind of backed off. I didn’t get the sense there was the fire in the belly,” said Curtis Watkins, the Republican chairman in Mecklenburg County, N.C.

Bush, now down to fourth place, might well have lost even if he had run a perfect campaign. His views on immigration are sharply at odds with the Republican base. His elevator pitch — experienced office-holder who gets things done — is a poor fit for an election year in which voters appear to prefer flame-throwing outsiders.

“I think he’s talking to an uninformed electorate that does not understand the complexities of governing,” said Phillips. “The electorate is angry, and it’s not sure what it’s angry about.”

And then there is that surname. “For good or for bad, people just don’t want to see another Bush in office,” said Valerie Earnshaw, the Republican chairwoman in Bedford, N.H. “I don’t think it’s anything personal. I think he has a lot of good ideas.”

Bush left office in 2007. He has appeared flummoxed by the rise of Trump, who sometimes seems to like taunting Bush on Twitter more than trying to be president. One by one, Trump has exposed Bush's weak spots: his brother’s record, his reliance on wealthy donors, his connection to failed Wall St. firm Lehman Bros. Every Bush response has fallen flat.

“The politics have changed, the campaigning has changed, the way you grab attention has changed,” said Watkins. “I think that’s something that Jeb may not necessarily embrace.”

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Last year, Bush said he would only run if he could do it “joyfully.” He is betraying no joy at all any more. He became downright whiny on Saturday, complaining about having to spend his time arguing with candidates he said would “get nothing done.”

“I’ve got a lot of really cool things I could do other than sit around, being miserable, listening to people demonize me and me feeling compelled to demonize them,” he said. “That is a joke. Elect Trump if you want that.”

Barring some miracle, Bush will be doing his unspecified cool things pretty soon.