THERE’S A new requirement for traveling to the United States: Turn over your social media account names — all of them, from the past five years, possibly to be stored for decades more.

A State Department policy that went into effect recently requiring visa applicants to provide authorities with their online identifiers is, in some ways, not a startling change. The Obama administration already asked some visitors to voluntarily provide their platform handles, and even when account names are not shared, authorities obviously have the wherewithal to seek out applicants’ public activity online. Officials in this administration had also started to require some categories of visa applicants to hand over the data. That affected about 65,000 people per year. Today’s policy will affect about 15 million.

It is the vast reach of the rule that has alarmed observers, along with the absence of an explanation of how the information will be used. There are certainly circumstances under which consular officials reviewing visa applications would want to look at a would-be traveler’s social media to verify a fact or to follow up on a security concern. But systematically reviewing the accounts of anyone who seeks to enter the United States is, according to the government’s own pilot programs, unlikely to be effective — and likely to chill speech on communications platforms essential to everyday life.

The chilling risk is heightened under a White House that has given people reason to think they should be careful. President Trump started his campaign by declaring that Mexicans are rapists. He kicked off his time in office by trying to keep many Muslims from entering the country. One criterion his administration hopes to consider in an overhauled immigration system is whether a citizen-to-be has demonstrated an interest in “patriotic assimilation.”

A Yemeni journalist working for the Associated Press was recently denied a visa to travel to New York to accept the Pulitzer Prize for international reporting. The State Department had no comment on the reason. A negotiator for Palestinian rights who has long been visiting this country also had her application rejected.

The security imperative of any vetting mechanism must be weighed against the risk it poses to keeping the United States open to people of all countries, cultures and political persuasions. Before it asks for millions of people’s personal information, the Trump administration should prove it has gone through that calculation and come out on the right side. Its record makes that impossible to take on faith.

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