Saudi Arabia and Dubai also send planes to American airports daily. It would be far easier, to arm one or more of these planes, with any number of different kinds of weapons, including dirty bombs, than to have anything funny going on in the container terminals.
Sorry for saying owning, but ultimately I don't think it matters whether they own or lease a termnal. As when "the Japanese" bought Rockefeller Center, it is not like they could take it home if they got mad at the US.
Similarly whether they own or lease these terminals, the terminal stays in the US and is operated according to US law and under the eye of US security authorities.