As Republican candidates began televised debates last summer, the Republican campaign strategist Mike Murphy invented a term for Donald J. Trump: “zombie front-runner.”

Mr. Murphy, the architect of the campaign of Jeb Bush, the former Florida governor, insisted that voters would tire of Mr. Trump’s antics and gravitate toward conventional candidates in the Republican primaries.

It never happened.

Now the longtime strategist is watching, like everyone else, to see what Mr. Trump will do next. And he replays what he might have done to block the rise of Mr. Trump, the presumptive Republican nominee, who has his party on edge five months before Election Day.

The pro-Bush “super PAC” that Mr. Murphy directed had more than $100 million to do it with. Some Republican peers have argued that he should have used the money to blast Mr. Trump from the start, but Mr. Murphy insists that would have only benefited rivals like Ted Cruz and Marco Rubio.