This is an interesting question. The freedom of religion is protected by the first Amendment of the Constitution of the United States:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.
This in itself would therefore indicate that the USA are a country, which displays a lot of tolerance towards people of a different religious background.
However, in recent years, there have been increasing instances of American citizens feeling threatened by certain religions, especially Islam. Since 9/11, a terrorist attack undertaken by members of the Muslim faith, Islam has often been directly associated with a threat of terrorism. This link has continued to grow since then, especially in connection with other terrorist attacks that have been committed by radical Islamists in the Western World, such as the London bombings in 2005 or the attack on a Christmas Market in Berlin, Germany, in 2016. The actions of extremists have sadly led to a growing fear and paranoia towards members of the Muslim faith in general. Therefore, it can be said that this has resulted in a decrease of tolerance in the United States towards followers of Islam. However, this is not unique to the United States, as this growing Islamophobia is also noticeable in other Western countries as a result of the events described above.
All in all, however, it is important to stress that the United States is still very tolerant compared to other countries, where members of certain faiths are actively persecuted, tortured and killed.