The sting operation was put in place via a Russian attorney/operative named Natalia Veselnitskaya whose social media history marks her as an adamant anti-Trumper and who was granted a special exemption to travel into the United States by the Obama Department of Justice. The sting was further facilitated by a Russian-born American citizen named Rinat Akhmetshin who was granted citizenship during the Obama era and who as as D.C. lobbyist is well-connected to the D.C. political establishment and is said to have been instrumental in the creation of an anti-Trump dossier Trump’s political opponents were preparing to use against him during the campaign. (And then sought out and turned over to the FBI by anti-Trumper John McCain)
It appears that once Veselnitskaya received confirmation she would be granted an audience with Donald Trump Jr. and other members of the Trump campaign, Obama Attorney General Loretta Lynch ordered an illegal recording of that meeting as outlined here by a breaking report from Jack Posobiec:
Scoop: Manaforts phone was illegally bugged during meeting with Russian Lawyer, confirmed by multiple sources. Lynch ordered it.