It did ok, but lets not get carried away either. It was a consistent no.3 after XBox and far behind the PS2 in the US. 

In 2003 GC outsold XBOX in the US... GC VS XBOX was a very interesting battle, and was not easy for XBOX this battle.

PS2 well... PS2 was PS2... but December 2004 was very close for all 3, XBOX did even better!

I don't remember the exatly numbers, but was some like GC above 800k, PS2 above 900k, and XBOX above 1 million...

EDIT

XBOX: 1,044,000

PS2: 989,000

GC: 814,000

It shouldn't!:P  It's very expected!

GC by that time was at 99$,-100$ from it's initial price!199$->149$ in 2002 149$->99$ in 2003!:P The 60% of its LT sales came in these two years!:P

N64 was the last "traditional" Nintendo console (ie: not relying on casual gamers) to do well in the US. The N64 shipped 21.9 million in the Americas versus 12.9 million for the GameCube ... so that was quite a hefty drop off.

Nintendo giving away the FPS market by not making a proper successor to GoldenEye/Perfect Dark hurt them big time.

GameCube looks good versus the Wii U, but that probably speaks more to how horribly the Wii U is doing. 

Holy hell, Wii was a beast. Amazing. Wii U is gonna sell below GC if they don't release more games. I think that with Zelda, Animal Crossing, and a Console Pokemon, the Wii U might beat GC.

Wii U selling below GameCube is a forgone conclusion. 

Wow, I never knew it! I guess the problem was quick support and weak sales for the rest of the world. When I look at the GC, I always think that Nintendo should try to release their biggest franchises faster on their next console, cause it worked out pretty well for the GC in its first years.

It is easy to come to such a conclusion but let's wait for Nintendo to put out everything they have. So far, the biggest hits are NSMBU, Mario Kart 8, Smash Bros. 4, and Mario 3D World...only 4 titles. Let's wait for the other ones to show their faces. I know, that it is hard to even fathom Wii U beating Gamecube at this point but I've seen stranger things happen in the gaming world.

Those are all their hit IP. 

Zelda and Animal Crossing generally don't sell 1/3 of what Mario Kart does on home console. Given Hyrule Warriors and Wind Waker HD and Link in Smash and Mario Kart, there's probably a large chunk of the Zelda fanbase that already owns the Wii U too. So that's not going to cause a monstrous boost. 

If MK8, Smash, 2D Mario, 3D Mario, DKC, and Splatoon have all come and gone and not been able to even get the system to sell at a decent baseline (40k this past month in the US is horrific) then Zelda and Animal Crossing sure as hell aren't going to do it. 

The "strange things have happened" part would have to be something like Splatoon becoming the next Minecraft/Pokemon/Wii Sports and selling for months and months and months bringing in millions of new consumers who wouldn't have bought the system. 

Just for reference sake these were the best selling Nintendo published Wii titles from last gen

1. Wii Sports

2. Mario Kart Wii

3. Wii Sports Resort

4. New Super Mario Bros. Wii

5. Wii Play

6. Wii Fit

7. Wii Fit Plus

8. Super Smash Bros. Brawl

9. Super Mario Galaxy

10. Wii Party

11. Mario Party 8

12. Mario & Sonic @ The Olympic Games

13. Super Mario Galaxy 2

14. Donkey Kong Country Return

15. Zelda: Twilight Princess

Wii Sports, Wii Fit, Wii Party, Mario & Sonic, 3D Mario, 2D New Super Mario, Donkey Kong Country, Mario Party, Smash Brothers, and Mario Kart are all on the Wii U. 

The only IP that doesn't have a new franchise installment already available on the Wii U is the Legend of Zelda mainline series, and that's the lowest in the top 15 IP that Nintendo had last generation. There's Wii Play as well, but I guess you could consider Nintendo Land it's equivalent. 

I'll give the Wii U one thing; it's always there to give me a hearty chuckle.