Sentence:  British journalists shun complete respectability, feeling a duty to be ready to savage the mighty, or rummage through their bins. Elsewhere in Europe, government contracts and subsidies <WSD>ensure</WSD> that press barons will only defy the mighty so far. 
Meaning of the word marked with <WSD> tags:  To make sure or certain of something ("usually" some future event or condition). (from 18th c.)