It's always been a popular sport in America for amateur players, kids, and women (our women's team is the best in the world). Men's soccer on a professional level is trending upwards, though. In college towns and the like you'll see a handful of people wearing Man U shirts or something. MLS is expanding, and in some cities it catches on rather quickly (Seattle, for instance).

It's still hampered by the fact that we have pretty third-rate players by international standards. The American leagues for gridiron, basketball, and baseball are de facto world championships because the best players in those sports always play here, but in soccer the best club could be English or Spanish or German or Italian, and Americans have a problem with that.

I would say it's a top 4 sport already (displacing hockey) but the top 3 is hard to break into. I suspect it'll displace baseball next.