Is America ruled by fear? Four recent harmless mistakes result in four more horrific shootings. Why has the US become a place where people shoot first and ask questions later?
Shot for knocking on the wrong front door
Recovering: The man who shot Ralph Yarl, 16, has now been charged with criminal offences. Glossary
Lobby - Lobbyists seek to influence politicians and lawmakers on specific issues, such as farming or healthcare.
Constitution - A document that sets out the fundamental rules according to which a country is governed, which are usually difficult to change.
Senator - A politician who has been elected to a body called a Senate. In the US, one of the two houses of Congress is the Senate. Ancient Rome also had a senate and senators.