Gun politics - the right to keep guns is protected by the Second Amendment. However, the amount of guns in the United States is large, and some political commentators argue that this is one of the causes of the increasing amount of mass shootings in the country. This is why people on different political aisles have called for more gun regulation, while others oppose these measures.
Abortion - this is a hot button issue up to this day. People disagree on everything here: whether a fetus is a human being or not, whether women should keep unwated pregnacies or not, whether the argument should be framed in a religious fashion or in a secular fashion, etc.
Recreational drug use and legalization - Drug use is still frowned upon by most of society, but this has not stopped marihuana from being legalized in several states. Many economists support legalization because they believe that prohibition only leads to inflated prices in black markets that are prone to violence. Legalization of hard drugs such as cocaine and heroine, however, is much more controversial.
Separation of church and state - Some people believe that United States is a Christian nation, and that the church should have a lot of influence in the government, while others argue that America is a secular country, and that state and religous matters are separate.