Mr. Johnson was booed by delegates at the Libertarian Party convention Friday during a preliminary debate after he described Mr. Weld's candidacy as "beyond my wildest dreams" and called the former Massachusetts governor "the original Libertarian."

Mr. Johnson's comments came after Austin Petersen, a consultant who's also running for the party's presidential nomination, criticized Mr. Weld for endorsing Republican Mitt Romney in 2012 instead of Mr. Johnson, who was the Libertarian presidential candidate.

"Why didn't your VP pick endorse you?" asked Mr. Petersen — who has called on delegates to stop nominating "failed Republicans" — at the nominating convention in Orlando, Florida.