It's funny, I'm 36, been playing hockey since 92. In my lifetime I think hockey had steadily gotten more popular in the US while the NHL had continuously gotten less popular. It's the best sport with the worst major pro league.
Most professional sports are showing declines in interest (the outliers being the WNBA and MLS only because they are comparatively new) which is attributable to many things, including the availability of other entertainment options, high cost to actually attend games which shuts out a large portion of the population, long-term interest fatigue, etc., etc. & etc.
Meanwhile, youth and collegiate hockey seem to be growing at a pretty good clip in the U.S., probably due in no small part to NHL expansion. Heck, even the University of Nevada Las Vegas now has a hockey team .... the mere idea of which would have drawn hearty laughter even just 10 years ago.
Hockey will only touch a relatively small niche part of the U.S. market -- every U.S. high school large and small has a football field, baseball field, and indoor basketball court, but hardly any have an ice rink -- though even a modest percentage of 330 million folks is still quite something.