In Texas, a poll watcher has to be a qualified voter in the county in which the election takes place. That means one must be a US citizen, resident of the county, and registered to vite at least 30 days prior to the election.
That’s the law in almost all places. Not sure what they did in 2012. Probably political parties sponsored guest observers who had no official poll-watching duties or powers. Even so, plenty of states would not seem to allow even that much.