Gundam in the US has been somewhat less than a big success. While Gundam has been immensely popular in Japan for over 25 years (spawning countless TV series, movies, graphic novels, books, toys, models, etc.), its popularity in the US didn't start until Gundam Wing (an alternate retelling of the basic Gundam story that was released in Japan in the 1990s) was released in the US. Wing was a big hit, and Bandai began saturating the US market with all things Gundam. The original Gundam series, several related side stories, and the series Mobile Fighter G-Gundam were all released on DVD, with all but the last few episodes of the original series airing on Cartoon Network (although most of what they aired was edited to some extent). The toys and model kits made their way to stores (mostly Toys R Us), where they sat on the shelves until they were marked down to clearance prices (and many still sat after this). The latest "original" Gundam series, Gundam Seed, eventually made its way to the US on DVD and in a bizarrely edited form on Cartoon Network (which, after poor ratings in a Saturday night time slot, eventually moved the show to a 1am Friday night/Saturday morning time slot, where ratings actually improved). Mobile Suit Zeta Gundam was released in a limited edition DVD box set (only 5000 copies were made), but it failed to sell out even at that low production run and a street price of only $120 (which is dirt cheap for a 50 episode anime series, especially one as popular as Zeta). (Note that Zeta is now available in individual DVDs.)
The current state of Gundam in the US is uncertain. There is not enough demand for models and toys to justify a retail presence (especially considering that the import versions are readily available, often for less than what the domestic versions would cost), and television simply isn't drawing in viewers (at 1am, you're not going to attract too many new fans). Bandai has committed to releasing DVDs and manga in the US, and its recent price drop on older shows (street prices are down to between $9 and $12 per disc, with box sets available at a further discount) are making DVDs a viable alternative to free but mostly unavailable and irritatingly edited television broadcasts. For the foreseeable future, DVDs, manga, and imports (and possibly some video games) are going to be the only source of Gundam in the US, which will satisfy existing fans but will do nothing to grow the fanbase.
What can be done to change this situation? Unfortunately, there isn't much that can be done now. Two key factors kept Gundam from attaining the kind of popularity it has in Japan.
First, Bandai waited too long to bring Gundam to the US. In the mid 1990s, there wasn't much competition in the US anime market (I mean, Power Rangers even became a hit). Domestic animation was winding down, and there was a gap in the market, particularly in the older demographics (attempts to match the success of The Simpsons had failed miserably - Fish Police anyone?); South Park, Futurama, and Family Guy had yet to appear. Anime was mostly a niche fad with very little dubbed material available (and what was dubbed was probably done poorly). Things like Power Rangers and Pokemon were making their way over, but there was room for more. Voltron proved that a more mature anime franchise could do well in the US (following the last Voltron's Japanese run, additional episodes were made for the American market), complete with lucrative toy sales. Unfortunately, while the US had probably been ready for Gundam for a decade, it just didn't happen. By the time Gundam Wing was released in the US, the older animation styles and more detailed storyline of the original made it less accessible to potential new fans, ensuring that a surge of popularity like there was for Wing would never happen for the franchise as a whole. The continued success of the alternate universe Gundams depends on a strong base in the original, which is lacking in the US (Cartoon Network never even made it through a single complete run of the original show and currently has no plans to air Zeta). With anime of all kinds now flooding the US, Gundam is relegated to nostalgia, without a fan base to be nostalgic about it.
Second, and more frustrating, is how the more mature content in Gundam is handled in the US. Gundam isn't adult anime by any means, but it features war, violence, death, love, and yes, even a little (very little) real or implied nudity. Cartoons are still thought of by many as light and fluffy (which isn't historically accurate, but the "protect the children" bunch conveniently forgets this), so blood and sex are forbidden. Add to this a complete lack of any consistent editing, and you end up with butchered Gundam shows (and neon lights on handguns sometimes but not always...). The editing does detract from the storyline and confuses new viewers. At least Wing was shown unedited in a midnight time slot, but aside from Char's Counterattack, no other Gundam show has aired without the sometimes senseless editing.
Perhaps the best solution for Bandai is to keep up the US releases of DVDs and Manga (at reasonable prices) in the hopes that these will drive demand for imported toys, model kits, etc. One of the benefits of the internet is that it allows niche markets to survive by breaking down geographic barriers - one small shop in California, Florida, New York, or anywhere else can sell to the entire US market, allowing them to focus on specific types of fans and provide specialty items that don't sell well enough for a large retailer to carry. With an existing fanbase and a continued presence in at least part of the domestic entertainment market, the Gundam franchise should be able to survive quite well. Perhaps the next incarnation of Gundam could be a big hit, but it is expecting too much to think that Gundam can return to where it was in the Wing era overnight.
Some thoughts on the US Gundam market from Bandai's President/CGO can be found here: http://aeug.blogspot.com/2005_11_01_aeug_archive.html#113309687243397038
Ueno's comments seem to indicate that Bandai doesn't really know how to attack the US market. He seems to think it's a matter of war themes not playing well in the US, but I still say it's just a matter of a fringe fanbase and competition with more entrenched brands. The idea of a Gundam show aimed at the US isn't a bad one, but I would go a step further and go for an updated version of the original. The original story is what the Japanese fanbase is built on, and that is where the majority of the merchandise is. The animation quality of the original Mobile Suit Gundam is just too dated; Zeta, CCA, 0080, 0083, 08thMS, etc. can all hold up on their own, but without the original, you will not build a coherent fanbase. The other big problem is Cartoon Network. Even popular brands like Transformers can't get decent time slots on Cartoon Network, so of course Gundam is going to die there. Given CN's track record with Gundam (both in first airings and reruns), it would be a mistake to count on them to build the franchise. SciFi would be a better choice; if they'll air Tripping the Rift, they shouldn't have a problem with a good Gundam show. The only problem is making a good Gundam show that will have an impact on the US market. Until then, it's DVDs, manga, and imports for us...