Except for the use of the informant as part of the justification for the FISA warrants wiretapping Trump associates, which lead to the unmasking of non-targeted individuals by Susan Rice, and the subsequent leaking of those conversations with names to the press.
And on another point, the difference between a spy and an informant.
An informant tells investigators what s/he knows. A spy gathers information to tell investigators.
Stefan Halper was going from campaign aide to campaign aide, asking probing questions. That is the modus operandi of a spy, not an informant.
“That is the modus operandi of a spy, not an informant.”
Halper was a professionally trained spy, in the pay and under the orders of a world-class spy agency, conducting classic HUMINT spy operations.
What actual spies do to gather Human Intelligence, is recruit sources who have access, and then manage them. There is a large element of grooming and psychological manipulation - targets are typically assessed by teams before being approached, to determine what would be most effective at controlling them (flattery, blackmail, bribes, ideology, etc.).
The professional spy (case officer) is the handler, the people on the inside are the assets/informants.
Halper came at his targets with a typical broad array of spycraft tools, appealing to their ambition and egos, greasing them with nice trips and lucrative side jobs, buying the drinks and bringing a honeypot woman (Azra Turk, whose image seems scrubbed from Google). Professional spies typically seduce their assets.
The recruiting and manipulation power of this classic spycraft is such, that even those serving life sentences for spying, still like their handlers personally. People are seldom catered to by such broad spectrum psychological gratification, as that provided in a tailored package designed by a world class spy agency.