As many times as they want, as long as they're only married to one person at a time.
As many times as they wish, as long as they are only married to one person at a time.
As many times as you can get divorced.
In the United States there is no limit, however, you can be married to only one person at a time.
As long as you are only married to one person at a time, you can get married as many times as you wish.