Secondary source opposition research largely consists of so-called votes-and-quotes — a political figure’s policy positions and past comments that have appeared in the news media. The material may lack the shock effect of original material, but it can be just as memorable.

Which brings us back to Mr. Romney — and his Irish setter, Seamus. The Romney family, as many readers of a certain columnist at this paper will recall, stowed Seamus on the roof of their car during a family vacation. This anecdote was but one element in a biographical series that The Boston Globe ran on Mr. Romney in 2007, when he first sought the White House. But it found new life when Mr. Romney became the Republican nominee in 2012.

It was the sort of story that, by the standards of an earlier political era, counted as peculiar behavior.

O.K., so how does it work?

The back-and-forth between news source and reporter over opposition research can recall adolescent flirtation: initial awkwardness, then apprehension over whether there is mutual interest — and neither party wants the world to find out the details of the courtship.

A reporter would rather not be identified as being spoon-fed information. Most sources do not want their dirty work to splash back on their candidate or party. So both parties have an interest in keeping a story’s genesis under wraps.

Typically, a campaign or government official approaches the journalist. This often begins with a request for anonymity, or in the parlance of the business, “No fingerprints.” The more sensitive the information, the more likely the pitch is made in person or on the telephone. Most political actors — not, apparently, Donald Trump Jr. — fear creating an email trail, at least before guarantees of anonymity have been offered.

After a reporter agrees not to reveal the identity of the source, the reporter and his or her editors or producers will confer about whether they are interested in pursuing a story about the material on offer.