Using the "correct" word is such an important part of politics but i feel like in recent years, it is what has brought politicians, presidents and laws under high scrutiny.
Whenever I hear the phrase "illegal alien" I always laugh because I think it is such a bizarre label. Illegal alien is supposed to mean undocumented immigrant but comes off more like a racial slur. It is a phrase most commonly used by the US government in federal documents. Because of semantics when I hear the word alien I think of someone from another planet or extraterrestrial, not an immigrant who doesn't legally reside in the states. More so, the term "illegal alien" is considered pejorative by most immigrants. I think the label somewhat dehumanize immigrants through context and tone, especially in the latino community.
During Obama's campaign for president he used the term "undocumented immigrants", after being elected he switched to "illegal immigrant". For a person who always says, "words matter", I find this sudden change pretty interesting. To hear how Obama explains why he uses the term "illegal immigrant", go to this site.