To enter into or prepare for a lengthy war, battle, or conflict; to adopt a combative or warlike position. While the true origin is uncertain, the phrase was popularized in English by The Godfather novel and films, where it referred to warring mafia families housing their soldiers in small, secure apartments to await orders. While Republicans have shown some flexibility over other contentious issues, it looks as though they're ready to go to the mattresses over the issue of gun control. We'll go to the mattresses if that's what it takes to defend ourselves!