Did the Queen have to give Royal Assent to the act which allows Prime Minister Theresa May to leave the EU?
Yes, if she wants to keep her job. If the monarch refused to sign a bill which had Parliamentary approval it would cause an enormous constitutional crisis, would directly challenge the sovereignty of Parliament, and could well threaten the role of the monarchy altogether.
Following the firing of FBI Director James Comey by President Donald Trump, Democrats and others have been calling for a "special prosector" to be assigned. What is a special prosecutor and what do they do?