Senator JD Vance was unsure where to stand or where to put his hands.

With a fresh haircut and a closely tailored blue suit on his first day of solo campaigning as the Republican vice-presidential nominee, Mr. Vance walked to the back of his chartered airliner to chat with reporters on Monday. Briefly uncertain of how to start, he furrowed his brow and looked from side to side.

His unease was understandable — the utilitarian design of airplane seating does not exactly facilitate group discussion — but also revealing.

Where a more seasoned politician may have simply leaned against a seat, Mr. Vance in his initial confusion hinted at the inexperience of a 39-year-old embarking on his maiden national campaign just one year after being sworn in to his first elected office. When a flight attendant approached and urged everyone to fasten their seatbelts before landing, Mr. Vance plopped into an empty seat in the press cabin and quickly buckled up — as if he were just another passenger, and not the only one inside the plane with his name on the outside of it, too.

The in-flight candidate is, in many ways, a useful metaphor for the moment: a gifted yet fledgling political talent — whose calling card is his connection to the working class — adjusting to a new life with his own chartered Boeing 737 as the newly minted member of a Republican ticket headed by a three-time presidential contender.

Mr. Vance had arrived in Milwaukee last week for the Republican National Convention not knowing if he would be picked as Mr. Trump’s running mate, and he left town at the end of it on his own chartered jet.

“When President Trump asked me to be his running mate, I really had no idea what was coming,” Mr. Vance said during his speech in Ohio. “I thought he might ask me, but I thought he might ask somebody else — there were a lot of good guys running.”