"We go blast Trump early, we'd move a lot of numbers to Cruz, a few to Rubio," Murphy said.
He regrets not proposing a joint attack on the "systemic threat" posed by Trump, but, in any case, he doubts super PACs that favored other candidates would have agreed.
"Our plan was to clobber him later," Murphy explained. "Well, we never got to later."
By late summer, Murphy worried that Bush's temperate, cerebral style "was the opposite" of what a decisive bloc of primary voters wanted.
Trump seized a larger-than-ever "grievance electorate," as Murphy called it, while adroitly tagging Bush as "low energy."
"It wasn't about energy; it was about tone," Murphy said. "It was a smart way for Trump, and his kind of weird savant gift he has to craft good insults, to take what was Jeb's strength as a president and make it a minus in the circus reality show of our debates."
He consoles himself with the fact that "we never said anything we're ashamed of," and he praises Bush for joining his brother, his father and the 2012 nominee, Mitt Romney, in refusing to endorse Trump.
"It's a pretty small list of people who are publicly willing to say, 'This guy should not be president of the United States,'" Murphy said. "I've been surprised at the magnetic field of blind party loyalty, and a little disappointed by it."
Trump has embarrassed Republican leaders most recently by invoking the "Mexican heritage" of the judge presiding over a lawsuit charging that Trump University defrauded students. Murphy advises vulnerable Republican congressional candidates to brace for more.
"They're thinking, 'All right, I've got primary voters who love Trump,'" he said. "'And I've got swing voters who can't stand the guy, who I need to win.'
"A lot of them are going to get in trouble because they'll get close to him, they'll back off, and it'll be inconsistent — which will not help."
Trump has hired experienced Republican handlers from the conventional campaign circles that Murphy has traveled in for a quarter-century.
The strategist Paul J. Manafort and the pollster Tony Fabrizio will help navigate the campaign's transition to the general election.
"They know how to do the basic mechanics," Murphy said. "But ultimately it's all about Trump. They can't change him."
Trump must appeal to a vastly larger and more diverse group of voters than in Republican primaries. His tactics so far — including controversial comments about women, Mexican immigrants and Muslims — have alienated many Americans. A New York Times/CBS News poll in May reported that 55 percent of those surveyed had an unfavorable view of him.
To win, Trump "would have to dramatically change the perception people have of him now," Murphy said.
He doubts that is possible, and that's why he still considers Trump a "zombie" candidate.
"He's the strength of the Trump campaign," Murphy concluded, "and he's the fatal flaw."