If it’s too cold for lions, why not introduce a couple of thousand Siberian Tigers? That might spice up the annual pilgrimage to Yellowstone.
In the west, there still are cougars (pumas, moutain lions, etc., they have so many names), but apparently they don’t behave like African lions. At one time, didn’t they inhabit the mid-west? I think they’re more solitary, whereas female African lions stay together. Males, however, are more like moutain lions, I believe. Anyway, I think mid-west winters are unduly harsh, both for lions and people.
There have been a couple of isolated cases of Mountain Lions in Vermont in the last few years.
Pumas formerly ranged as far east as the eastern seaboard. As they tend to like cover (forest, brush, and scrub), I would guess that on the Great Plains they may originally have lived mainly along watercourses.
African lions are mainly found in savanna or lighter forest. They are not found in heavily forested areas, such as the larger blocks of rainforest.
You could wager on the grizzlies vs tigers. 
I know I’ve been sily in this thread already, but please: can we leave tigers out of this? They are extremely difficult to find in the African wilderness. In fact, I’d be willing to bet that you couldn’t collect enough African tigers to populate a single cage, let alone the American mid-west.
OK? So no more about TIGERS!!! GRRRR!
No, it’s an excellent idea. If you read the article they are talking about restoring species that were here in North America and went extinct only 10,000 years ago. It would be no more harmful than the reintroduction of the wolf or bison.
There was a highly diverse large mammalian fauna in North America, similar to that which occurs in Africa today, during the Pleistocene. Many scientists believe that overhunting by humans was at least partially to blame for the extinction of many of these species.
North America formerly had something like 5 species of elephants, tapirs, lions, hyenas, cheetahs, horses, several kinds of llamas, a variety of antelope-like forms (of which the pronghorn is the only survivor), not to mention several species of giant ground sloths (which I would really like to see reintroduced if you could find any).
Perhaps we could find them on the Asian continent?
Somehow I don’t think the ranchers would be the biggest problem. People flip out and keep their kids home from school when a solitary mountain lion (puma, cougar, painter, panther…) is spotted within a few miles of a populated area. I can just imagine how folks would feel if you were releasing predators three times that size that travel in prides and cooperate to take down kills. And what would introduction of lions do to existing apex predator populations?
As for the elephants, I certainly wouldn’t be thrilled if an elephant stomped down my fences and ate my apple trees. They wouldn’t be eating livestock, but they can be amazingly destructive critters.
You forgot the giant running bears, giant bison, giant beavers, saber-toothed cats, and dire wolves.
Allow me to reiterate. I lived acrosss the road from and worked at The African Lion Safari Game Park Whatever problems the animals might face, the cold is not one of them.
I didn’t forget them. I was mainly talking about fauna that was similar to that found in Africa and Asia today. I also deliberately left out Glyptodonts, giant Capybaras, giant armadillos, Terror Birds, and Thunder Birds.
There is also one in Arkansas, but they keep them inside during cold weather.
They have male African elephants.
Those guys are huge. I know I wouldn’t want them living in the wild.
http://www.elephantsanctuary.org/default2.asp
Some of their information is out of date. The young African male was on Animal Planet last year.
Given a choice, I’d prefer that these were kept in South America.
Keep in mind the square-cube law. An animal the size of an elephant has very little surface area for its volume, which makes it hard for them to radiate much heat into their environment. The ears might be a problem, especially if we’re talking African elephants (whose ears are so large precisely to increase their surface area for heat radiation), but other than that, an animal that size will have no problem with low temperatures.
On the ecological note, just because these beasties or ones very much like them used to be here doesn’t mean that re-introducing them wouldn’t cause a problem. First of all, we’re not bringing in analogues to all of the pleistiocene fauna, since some of them don’t exist any more. Maybe the mastodont populations were naturally kept in check by the smilodons, for instance. OK, a modern elephant isn’t too far off from a mastodont, but with what do we replace the smileys? And even if we brought everything back, we’re not bringing them into an ecological vacuum. There are plenty of species currently living in North America, some of which probably weren’t here in pleisiocene times. Could they survive a rolling back of the clock?
Oh you’re no fun.
Terror Bird Titanis walleri. Estimates range up to 9 feet tall. They were running around in Florida not all that long ago.
Thunder Bird Teratornis merriami. The biggest species in North America, Teratornis incredibilis, had a wingspan of up to 18 feet. It had even bigger relatives in South America with wingspans up to 23 feet.
That Terror Bird looks like good eatin’.
Yeah, but you got to catch it first. It might be just a little bit more of a challenge than your average Bob-white.