I have to agree with Plaw here (despite his incessant thread "bumping" to make people pay attention :p ), that if the President has the power to block this deal, he should. I wouldn't have a huge problem with this normally, should it be a company that was independent of a foreign government, or a reliable government known to be friendly to the United States (i.e. the UK). But when it is subsidized by the UAE, who have high government officials known to be friends of Osama Bin Laden, I simply cannot see how there would be no security risk involved. It would be like leaving the inmates the keys to the asylum, so to speak.
Again, as Fathersson has already mentioned, there are already plenty of foreign companies controlling U.S. businesses and assets. However, in this particular case, the company is directed by the government that is not only related to terrorists, but also with a country that is notorious for its drug shipments to Asia.
As we've already said, this isn't like a foreign company is coming in and making an offer to the U.S. - they are buying out the UK company, which, I would think, legally leaves the United States' hands tied if there is some sort of contract with the original company. If the President interfered in a business deal simply because we objected who was taking over a company, I would think that would be overstepping his bounds. It would be like telling a Finnish company not to buy out a Swedish one because we don't like the Finnish - we really have no jurisdiction.
In the end, does the President have the power to stop an international business deal because of who will be taking over another company? If we want to stop them from taking over our ports, wouldn't it make sense to just cut the deal short with the company and make a deal with a new, friendly company (possibly domestic!).