When US opposition started mounting last week to the planned purchase by Dubai's DP World of P&O's US container ports, it was not the first time a campaign had blown up in the US against foreign ownership of port assets.

However, efforts by a number of US senators to stop the deal could, observers believe, have far wider implications than the last such campaign, when Congress prevented China's state-owned Cosco container shipping line from taking control of a container terminal in Long Beach, California, in 1998.