Which poses a problem. The free exercise of Islam includes subjugating, enslaving or killing non-Muslims. The solution: declare Islam not to be a religion. It is a socio-political system masquerading as a religion.
The states can constitutionally restrict Islam (as a religion) all they want if their own state constitution allows. But the feds cannot constitutionally restrict Islam as a religion.
However, the political side of Islam is another story. If it can be proven that Political Islam presents a clear and present danger to the rights and peace of America and the American People, then I think the feds constitutionally could step in to treat Political Islam as a Hostile Invader and put them in Gitmo or deport them.