Congress succeeded this week in scuttling a deal that would have seen ownership of operation of six U.S. ports transferred from British to Dubai ownership. Never mind that a 45-day review, which would have determined if the ownership change had national security implications, had just begun. Never mind that port security is the job of the U.S. Coast Guard and Customs Service, not port operators, no matter what their nationality. Never mind that the United States needs foreign investment, to upgrade our ports and to float our growing national debt, now more than ever.

Lawmakers are irrationally considering going even further by proposing legislation requiring that all U.S. ports be managed by American companies, even though few U.S. entities remain in the shipping and port business.

This crazed xenophobia began several weeks ago when lawmakers learned that Dubai Ports World, a state-owned company in the United Arab Emirates, was close to finalizing its purchase of the British firm Peninsular and Oriental Steam Navigation Co. P&O operates terminals in New York, New Jersey, New Orleans, Miami, Philadelphia and Baltimore. It has some operations in Portland.

The House Appropriations Committee voted 62 to 2 to kill the deal and the Senate was likely to follow suit. Lawmakers had a point that the acquisition should have been more closely vetted by the Committee on Foreign Investment in the United States but they were wrong to oppose the deal.

On Thursday, Dubai Ports World announced that they were dropping U.S. ports from the deal. It remains unclear whether management of the U.S. facilities will be sold to another company or whether DPWP will form an American subsidiary to manage them. The rest of the deal closed on Thursday.

Here’s what Congress has accomplished. Dubai Ports World, and other foreign companies, will manage the hundreds of ports where cargo is packed to be sent to the United States (where, if you’re a senator worried about weapons being smuggled into this country, surveillance would be most helpful). They won’t, however, manage ports here where the cargo is unloaded and where port security is already the responsibility of U.S. agencies.

Lawmakers alienated an ally and reinforced the notion that America is anti-Muslim. Whether Middle Eastern companies retaliate by quashing deals with U.S. companies remains to be seen.

They may also have cut off an important source of port improvement money. According to Stephen Flynn, a former Coast Guard commander and a port security expert at the Council of Foreign Relations, U.S. foreign trade will double by 2020. To accommodate the growth, U.S. ports will have to expand and upgrade to handle 18 million containers a year, he told The Washington Post. This work, which Mr. Flynn estimates will cost $10 billion, can either be funded by taxpayers or shipping companies, few of which are American-owned.

If members of Congress were serious about port security, they would appropriate money for it and work with companies like Dubai Ports World to install scanning equipment in foreign ports. Instead, they used misplaced fears of terrorism to stop a business transaction without knowing what they were doing.