President Trump in the White House. (Jabin Botsford/The Washington Post)

David Bier is an immigration policy analyst at the Cato Institute.

President Trump issued a presidential proclamation this weekend instituting a new "travel ban" that restricts entry to the United States for nationals of eight countries. The president cites America's inability to screen out terrorists as the justification for the ban. But such a ban would not have kept out the 9/11 hijackers or any terrorists since then, nor would it have prevented any terrorism deaths in decades.

Not only do the purported threats lack merit; the vetting rationale does, too. The ban singles out nationals of Chad, Iran, Libya, North Korea, Syria, Venezuela, Somalia and Yemen. The purported basis for the proclamation is that most of these governments fail to share sufficient information about the identities of their nationals with U.S. agencies to, as the proclamation states, “adjudicate an application” for a visa by their nationals.

This premise is flawed. Under immigration law, the U.S. government doesn't need to obtain any information on visa applicants merely to process an application. That's because applicants bear the burden of proof in the visa process. If they cannot prove their identity and eligibility, visa adjudicators can simply deny them on an individual basis.

This means that the travel ban exists solely to deny visa adjudicators the opportunity to review each application. The president apparently doesn’t trust these trained experts to do their jobs. The proclamation provides no reason to doubt the integrity of consular officials reviewing visa applications, nor does it provide any evidence that they are failing to review evidence properly.

In fact, consular officials do ramp up visa denials for nationals of countries involved in civil wars. The denial rate for Syrians more than doubled what it was before war broke out in their country. This increase likely reflects the inability of applicants to obtain certain documents or to prove they will return to their home country when the visa expires.

Supporters of the president's travel ban may ask: If it's true that these foreign governments fail to cooperate fully with information-sharing, why not institute a blanket ban on their nationals and save adjudicators the trouble? The answer is because many applicants from these countries can still prove their identity and eligibility. That's what makes the ban politically necessary, even if it is legally unnecessary.

Tens of thousands of the nationals of these countries have already traveled back and forth peacefully to the United States. The U.S. government knows exactly who they are. Thousands of others have U.S. citizen family sponsors whose identity can be proven with a DNA match.

But there is a second major failure in Trump’s proclamation: It equates people’s “nationality” with their “government.” A person can have the nationality of a country that does not fully cooperate with the United States without ever having lived under the targeted regime.

Syrians and Iranians, for example, can be born abroad and live their entire lives outside of those countries and yet maintain Syrian or Iranian nationality. It's just incorrect to assume any connection between a government and "its people." Most countries in the world lack birthright citizenship, so it's possible that Syrian or Iranian nationality could be their only nationality.

Given these facts, the proclamation amounts to a White House override of the immigration screeners, preventing the entry of nationals of these countries who meet eligibility to enter. So it’s worth asking: How poorly have immigration screeners done?

The proclamation presents no evidence that mistakes are at all common for these eight nationalities or even for any others. In fact, only 34 people have legally immigrated to the United States since 9/11 and been either convicted of terrorism offenses or killed during an attempted attack. Of those people, a large share arrived as children; they and others were radicalized long after their entry. At most, only nine attempted to carry out an attack in the United States after being radicalized prior to entry. That's one potential terrorist per 41 million visa approvals or entries without visas since 2001.

There is only one post-9/11 terrorism offender who radicalized prior to entering the United States and who actually killed people: Tashfeen Malik, the Pakistani woman who participated in the San Bernardino terrorist attack in 2015. But Pakistan has never been subject to Trump's travel ban. And even if it were, one instance is hardly a trend.

There is simply no evidence that visa adjudicators aren’t doing their jobs. The president’s most recent proclamation is nothing more than a political document, not one with any legal or national security basis.