Some people are beginning to predict the breakup of the United States, see for example Igor Panarin who predicted it ten years ago but is now getting more attention, http://en.rian.ru/world/20081124/118512713.html
Any US states worth absorbing? How about Washington, Minnesota, Wisconsin, Maine and Vermont? Geographic contiguity and similar politics, economics and demographics would be necessary.
Maybe Alaska could come in as a territory and be renamed the Western Yukon, that was even less likely however.