Perfectly Legal Immigrants, Until They Applied for Citizenship.
Spend many years in the US, have a family, house, and a job. Apply then for the US citizenship. If the US government finds something they don't like, be prepared to be deported, what would not happen if you hadn't asked for the citizenship. The article above tells the sad story of a Philippine couple that is to be deported after 25 years as legal immigrants in the US.