AMERICA’S ONGOING retreat from the world, which dovetails with President Trump’s stated contempt for some of its poorest and most desperate nations, provides the context for the administration’s addition of six countries to the existing travel ban. The decision, effective Feb. 22, deals a blow to U.S. economic and strategic interests — to say nothing of the country’s already tarnished international image — on the basis of supposed security concerns for which officials have provided no evidence.

Nigeria, Eritrea, Tanzania, Kyrgyzstan, Sudan and Myanmar were added to the list for what the White House called “information-sharing deficiencies and national security risk factors.” That rationale requires a hefty dose of credulity given Mr. Trump’s views on visitors and immigrants from Nigeria, by far the most populous country added, who, he said, would never “go back to their huts” once they had entered the United States.

Never mind that the estimated 345,000 Nigerian immigrants living legally in the United States are an unusually successful cohort, with a significantly higher proportion holding college and graduate degrees than among the U.S.-born population. The president’s habitual racism is disturbing. Equally disturbing is his administration’s cavalier willingness to separate families — for that is the effect of denying entry to thousands of people who seek visas mainly to rejoin relatives living in the United States.

Only last summer, the Trump administration announced, largely in an effort to compete with China’s aggressive push in Africa, a “Prosper Africa” initiative with a goal of doubling two-way trade and investment with the resource-rich continent. Chances of achieving that goal will be undercut by expanding the travel ban to include Nigeria, which has Africa’s largest economy and population.

Administration officials cited the countries added to the ban, all of which have significant Muslim populations, for a variety of ostensible sins. They include the lack of updated passport systems, which, they said, complicate information-sharing with U.S. law enforcement agencies. But officials declined to provide instances of any specific security threats to the United States originating in those countries. Nigeria has engaged in military-to-military cooperation with the United States.

The existing travel ban, which covers seven countries, has blocked about 70,000 immigrants from obtaining visas since it was unveiled shortly after Mr. Trump entered office in 2017. Extending the ban, which will add thousands more to that list annually, fits neatly into Mr. Trump’s political calculus. The rationales vary, but the effect of his immigration policies is always to keep people out: Legal refugees, the annual ceiling for whom has been lowered by more than 80 percent; asylum-seekers, for whom the rules have been rewritten to bar their entry in most cases; poor people who might need temporary assistance; pregnant women; and many others.

In the case of the travel ban, “national security” is a handy pretext. But Mr. Trump’s goal is to shut off the spigot of plucky, hopeful and ambitious people who aspire to become Americans — and who, like every previous generation of immigrants, would greatly enrich the nation.

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