The United States has freedom of religion and cannot ban any religious group from forming a political group. People be up in arms if they said let's stop at a Jewish group from a making a political group. I think it's ridiculous and Islamophobic. People need to educate themselves for on religion.
No, Islamist political parties should not be banned, because freedom of speech is important to all citizens. It is important that Islamist politicians be allowed to engage in political processes, and laws can be put in place that require them to act peacefully. If all political parties are kept from sanctioning violence, any political group can lawfully engage in discussion and contribute to public discourse.