It was the first call that day in a series of conversations that ultimately spun out of control.

Mr. Trump was en route to a campaign rally in Waterbury, Conn., and he promised to call again in about 30 minutes. I was filing a story on Mr. Trump’s aircraft and was up against a tight deadline.

Mr. Trump’s fleet — two airplanes and three helicopters — is an integral part of the billionaire image Mr. Trump projects, and the aircraft are an effective prop on the campaign trail. They are also one of his campaign’s largest expenses. So far a company owned by Mr. Trump has been paid roughly $3.7 million by his campaign for costs associated with flying him to events.

The story I was working on took a close look at the aircraft — which, I was surprised to learn, were aging: four were more than 20 years old. Having covered Wall Street for years, I knew this was an anomaly among the super wealthy, who tend to buy newer aircraft, or lease or charter planes. (Mr. Trump had written in his book “The Art of the Deal” that older planes are good value. Others say he buys them because he really isn’t worth the $11 billion he claims to be.)

Presidential candidates frequently field reporter questions, but usually in gaggles. One-on-one interviews tend to be strategically planned, and candid moments are rare. Reporters do not typically travel with the candidate and do not get close to them at rallies.

Mr. Trump, though, is no ordinary candidate, and he often calls (and calls out) reporters who are writing about him, alternately charming and bullying them. My experience suggests Mr. Trump makes a calculated game-time decision on each call; if he thinks he will benefit from a given conversation, he engages. Stories that talk about his wealth, or question the size of it, seem to be of particular interest.