The Libertarian vice presidential candidate, William F. Weld, said Tuesday that he plans to focus exclusively on blasting Donald Trump over the next five weeks, a strategic pivot aimed at denying Trump the White House and giving himself a key role in helping to rebuild the GOP.

Weld’s comments in a Globe interview mark a major shift in his mission since he pledged at the Libertarian convention in May that he would remain a Libertarian for life and would do all he could to help elect his running mate, Gary Johnson, the former Republican governor of New Mexico…

While Weld insisted he still supports Johnson, he said he is now interested primarily in blocking Trump from winning the presidency and then potentially working with longtime Republican leaders such as Mitt Romney and Haley Barbour to create a new path for the party after the election.

“Maybe somebody is going to come up with a new playbook, and I don’t know who it’s going to be, but it would be fun to participate,” Weld said in a telephone interview from Atlanta, where he was holding a fund-raiser and rally and planned to watch and tweet about Tuesday night’s vice-presidential debate featuring his major-party rivals, Democrat Tim Kaine and Republican Mike Pence.