In order to vote in elections in the United States of America, you have to be a U.S citizen. You can not vote if you do not have a U.S citizenship. Green card holders can not vote until they become naturalized U.S citizens. In basic terms, if you want to have the right to vote in the U.S, you need to become a U.S citizen through naturalization (legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country).