He suggested banning folks with a particular religion from entering the country...that's some crazy dangerous fucked up shit. He has a bunch more crazy policies, but this is the most dangerous and frankly unheard of before Trump.
*Temporarily banning. He's since changed his tune, saying that we need to heavily scrutinize those coming from countries that are terrorist hot beds. Jimmy Carter did something similar, so don't say it's "unheard of."