Arizona, Connecticut, Delaware, New York, Oklahoma and Utah. Some 4.5 million independent voters – 2.4 million in New York alone – can’t vote because they aren’t registered party members.
Alabama, Arkansas, Georgia, Missouri and Tennessee. Voters can choose to cast a ballot in either primary.
California, Illinois, Massachusetts and New Jersey. Generally independents can vote for either party, although in some states, they must register with the party on Election Day.
Alaska, Colorado, Idaho, Kansas, Minnesota, Montana, New Mexico, North Dakota and West Virginia.
Read Independent voters may be vexed at polls for more information about "open" and "closed" primaries.