Elaborate. There has never been a difference. If the NSA overhears you talking about buying a brick of weed, they send that to the DEA, who does some parallel construction to find another reason to pull you over. Why wouldn't they cooperate? Do you have any reason to think that they didn't in the past?
Perhaps a better question is, if the FBI obtains a warrant to "wiretap" would that give them justification to do a narrow search on the pool of data already collected. Probably true that the collected data couldn't be used to initiate an investigation, but if the investigation is initiated through other means, what does that mean?
"What man has done, man can aspire to do." -- Jerry Pournelle, about space flight