Gov. Tim Walz of Minnesota traded the harsh lights of the debate stage for the more comfortable environment of a campaign bus tour on Wednesday through central Pennsylvania.

After his occasionally nervy encounter with Senator JD Vance of Ohio at the vice-presidential debate on Tuesday night in New York, it is not hard to guess which setting Mr. Walz prefers.

The clash with Mr. Vance, after a day of buildup over an inaccurate anecdote he has told often about being in Hong Kong when Chinese troops crushed pro-democracy dissidents in Tiananmen Square 35 years ago, highlighted a tendency to exaggerate his biography and speak imprecisely or inaccurately.

And on the biggest stage of his career, he was plainly an uneven surrogate. The version of the punchy Midwesterner who rocketed onto Ms. Harris’s ticket in part by branding former President Donald J. Trump and Mr. Vance as “weird” on national television was rarely seen when confronted by two probing moderators and a slick opponent untroubled by frequent twisting of the truth.

In fact, since Mr. Walz joined the ticket, the Harris campaign has almost entirely kept him off national television, negating what was seen as one of his greatest strengths.