I suggest you read the article you linked carefully. Follow the links to the articles of each of the constituent programs, and read those articles carefully with a critical eye. Pay particular attention to the number of interceptors those programs actually have, the type of missile those systems are designed to intercept, and the locations of the installations. You can use the "measure distance" tool on google maps to plot out great arcs to get an idea of what sort of threat those installations are meant to counter.

I'll sum it up for you: The US has some defense against countries like North Korea. Not against Russia, nor even China. But don't take my word for it, read those articles carefully, paying attention to the details.