ALTON, N.H.—Republican Jeb Bush started off his presidential campaign describing himself as a “joyful tortoise.” As voters leaned toward political outsiders, he dubbed himself a “disrupter.” Then he emphasized competence and went on the “Jeb Can Fix It” tour.

Mr. Bush’s latest incarnation: Trump slayer.

Inspired by his confrontational approach in last week’s debate toward front-runnerDonald Trump, Mr. Bush is seeking to revive his campaign by repositioning himself as the New York businessman’s leading nemesis.

He’s also accusing his rivals of being “intimidated” by Mr. Trump. A new campaign video mocks Florida Sen. Marco Rubio, New Jersey Gov. Chris Christie and Texas Sen. Ted Cruz—who are better positioned to win over Mr. Trump’s supporters—for not being as aggressive as Mr. Bush.

At a town-hall meeting here Monday, Mr. Bush jabbed Mr. Trump for praising Russian President Vladimir Putin and for disparaging Mexican immigrants.

Read the article “The Evolution of Bush’s Candidacy: From ‘Tortoise’ to Would-Be Trump Slayer” on google.com.