His warning, in an interview with The Sunday Telegraph, is doubly remarkable. Not only is he the first major figure from the Bush camp to warn on protectionism, but he was also the chief architect of the controversial Patriot Act that followed the 9/11 attacks.
Dinh – now a leading Washington lawyer and executive – says the act had been a double-edged sword, with its anti-money-laundering powers being used to impose new restrictions on foreign business and trade. American politicians, he says, are guilty of "national security protectionism".
His warning echoes comments from a series of non-US policymakers, most notably Alistair Darling, the Chancellor, who said recently: "There are moves in parts of the world – the United States for example – that look like pure protectionism."
It comes amid growing fears for the fate of the US economy, after the dollar plunged to a 26-year low against the pound and an all-time low against the euro.
"In a time of economic downturn you will always see the national tendency of the political process to favour more parochial interests," says Dinh, who is now professor of law at Georgetown University and principal of law firm Bancroft Associates. "You also have a continuing tendency to use the national security excuse as a means not necessarily of combating terrorism on the military front but of fostering economic protectionist measures. This is worrisome."
He pointed towards the recent episode when Dubai Ports World took over P&O but was blocked from taking control of a series of American ports following a major Congressional backlash.
"We are talking about a creeping protectionism that has no place in our international economic system," he said. "It is a disdain for the others, and a desire to protect our economy from outsiders. It does not recognise that the United Arab Emirates has been one of the prime partners of the US in its Middle East initiative, or that Dubai is probably more capitalistic than Boston.
"I think there is a lot of legitimate concern within the United States and outside that we have another form of creeping protectionism. It is a product of political demagoguery."