GATS and Port Management

Senator Clinton apparently has introduced legislation that would bar firms owned by foreign states from managing US ports. The bill is aimed at the takeover of P & O, a company that currently manages six US ports, by Dubai Ports World, which belongs to the United Arab Emirates. The purported policy motivating this legislation is the risk to national security posed by foreign ownership.
Several questions arise. Can this legislation be squared with US obligations under the General Agreement on Trade in Services? More to the point, is public ownership a valid criteria for barring firms from market sectors? What is more likely to endanger US security interests, giving an oil emirate a stake in a critical sector of the US economy or isolating it?
My own crudely political take: Roughly a year ago, my friend and former colleague Bill Stuntz proposed an alliance of political progressives and evangelical Christians across a number of fronts. One aspect of his rather Swiftian proposal was a commitment by the left to free trade as the best means to alleviate global poverty. It dismays me that a leading contender for the Democratic Party's presidential nomination feels the need to shore up her credentials as a protectionist.