You are permitted to bring a liter of alcohol through U.S. customs without any duty fees being applied. This is provided that you are over 21 years of age and legally allowed to do so.
If you have traveled from the U.S. Virgin Islands or the Caribbean, then you are able to bring in more than a liter. If you want to bring more than a liter of alcohol through U.S. customs from other destinations, then you need to declare it to customs officials as you pass through border control. You are then required to pay duty and federal excise tax on the alcohol.