de·rail 
(dē-rāl)
(dē-rāl)intr. & tr.v. de·railed, de·rail·ing, de·rails
1. To run or cause to run off the rails.
2. To come or bring to a sudden halt: a campaign derailed by lack of funds; a policy that derailed under the new administration.
[French dérailler : dé-, off (from Old French de-; see DE-) + rail, rail (from English; see RAIL1).]
de·railment n.