The problem they were having in Idaho is they introduced back the larger canadian grey wolf instead of the native timber wolf.
This is a line of nonsense that the anti-wolf lobby likes to throw around. Here is the real story.
Traditionally, Idaho's wolves were considered to be the subspecies
irremotus according to the Goldman taxonomy. The population of wolves in Canada that the Idaho transplants were drawn from were considered to be the subspecies
occidentalis.
Since then, wolf taxonomy has been revised and
irremotus is now included in
nubilis, the subspecies currently found in Minnesota. The subspecies
nubilis ranged across much of the western United States and into Canada where it bordered the range of
occidentalis. At the boundaries of subspecies there is often quite a bit of integration and hybridization. The
nubilis wolves living in Minnesota have quite a bit of genetics in common with another population,
lycaon which may in fact be a completely different species. So it is in fact more likely that the "original" Idaho wolves had more in common with
occidentalis than they did with
nubilis from Minnesota.
But the proof is in the pudding, as they say. The crux of the argument put forth by the anti-wolfers is that the "Canadian" gray wolves are "larger and more aggressive" than "native" Idaho wolves were. This argument doesn't seem to hold up, because in Idaho's 2009 wolf hunt, 188 wolves were "harvested" and the average weight of these animals came in at under 100 lbs.