@gollum,
Answer to your first question:
"This is a typical series of events when an illegal immigrant is arrested: The illegal immigrant will be held in the jail of the city, county, or parish in which they were charged; the jail will report the illegal immigrant to ICE. ICE will indicate to the jail and the D.A. that they want the D.A. to drop the charges. The D.A. usually drops their charges. ICE officers come to the jail. They take the illegal immigrant into federal custody. They place him or her in a federal detention center. And ICE then transports the illegal immigrant to immigration court."
http://immigration-law.freeadvice.com/immigration-law/immigration-law/arrest-immigration-consequences.htm
Answer to your second question:
"U.S. citizens cannot be deported. However, the government can attempt to take away the citizenship of a naturalized citizen if they can show that his/her naturalization application was "fraudulent" or contained certain omissions or mistakes (for example, if a person failed to disclose an arrest or conviction). A person whose citizenship is stripped may again be vulnerable to deportation."
http://www.miracoalition.org/en/resources/enforcement/deportation
If this answers your questions, please award this reply "best answer".