the constitution is the law of the land, to have any other law you would need to fully overthrow the government. within the US sharia law is just the inner workings of any Muslim faith when dealing with themselves or how they chose to deal with others. every religion and many groups do this. Mormons have Bishop's Court where they have local leaders meet with people who will decide if they will excommunicate someone for a particular sin or behavior like adultery or abuse, they may also use these formal proceedings to decide if the church itself will recognize a divorce or annulmemt within their own religion, the US government isn't involved in or forbidding Mormons from running these 'Mormon court of law' proceedings as everyone involved is legally free to not even give a shit or participate if they don't want to and it effectivly means nothing to anyone outside their church groups if it even means much inside those groups. but at one point the US government did go to war with the Mormon Church to stop them from taking over the country or some other fever dream because it was a good distraction from the upcoming civil war, and at some point Mormons were a huge voting bloc moving into areas and taking them over and electing their leaders into the highest offices they could and clearly they intended to become the dominate culture and religion of the US from the top down for a good while, but if a whole political party was constantly going off on how we need to ban Mormon Law before it takes over the country, you'd be right to laugh at them.